github.com/sanprasirt/go@v0.0.0-20170607001320-a027466e4b6d/src/reflect/value.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package reflect
     6  
     7  import (
     8  	"math"
     9  	"runtime"
    10  	"unsafe"
    11  )
    12  
    13  const ptrSize = 4 << (^uintptr(0) >> 63) // unsafe.Sizeof(uintptr(0)) but an ideal const
    14  
    15  // Value is the reflection interface to a Go value.
    16  //
    17  // Not all methods apply to all kinds of values. Restrictions,
    18  // if any, are noted in the documentation for each method.
    19  // Use the Kind method to find out the kind of value before
    20  // calling kind-specific methods. Calling a method
    21  // inappropriate to the kind of type causes a run time panic.
    22  //
    23  // The zero Value represents no value.
    24  // Its IsValid method returns false, its Kind method returns Invalid,
    25  // its String method returns "<invalid Value>", and all other methods panic.
    26  // Most functions and methods never return an invalid value.
    27  // If one does, its documentation states the conditions explicitly.
    28  //
    29  // A Value can be used concurrently by multiple goroutines provided that
    30  // the underlying Go value can be used concurrently for the equivalent
    31  // direct operations.
    32  //
    33  // To compare two Values, compare the results of the Interface method.
    34  // Using == on two Values does not compare the underlying values
    35  // they represent.
    36  type Value struct {
    37  	// typ holds the type of the value represented by a Value.
    38  	typ *rtype
    39  
    40  	// Pointer-valued data or, if flagIndir is set, pointer to data.
    41  	// Valid when either flagIndir is set or typ.pointers() is true.
    42  	ptr unsafe.Pointer
    43  
    44  	// flag holds metadata about the value.
    45  	// The lowest bits are flag bits:
    46  	//	- flagStickyRO: obtained via unexported not embedded field, so read-only
    47  	//	- flagEmbedRO: obtained via unexported embedded field, so read-only
    48  	//	- flagIndir: val holds a pointer to the data
    49  	//	- flagAddr: v.CanAddr is true (implies flagIndir)
    50  	//	- flagMethod: v is a method value.
    51  	// The next five bits give the Kind of the value.
    52  	// This repeats typ.Kind() except for method values.
    53  	// The remaining 23+ bits give a method number for method values.
    54  	// If flag.kind() != Func, code can assume that flagMethod is unset.
    55  	// If ifaceIndir(typ), code can assume that flagIndir is set.
    56  	flag
    57  
    58  	// A method value represents a curried method invocation
    59  	// like r.Read for some receiver r. The typ+val+flag bits describe
    60  	// the receiver r, but the flag's Kind bits say Func (methods are
    61  	// functions), and the top bits of the flag give the method number
    62  	// in r's type's method table.
    63  }
    64  
    65  type flag uintptr
    66  
    67  const (
    68  	flagKindWidth        = 5 // there are 27 kinds
    69  	flagKindMask    flag = 1<<flagKindWidth - 1
    70  	flagStickyRO    flag = 1 << 5
    71  	flagEmbedRO     flag = 1 << 6
    72  	flagIndir       flag = 1 << 7
    73  	flagAddr        flag = 1 << 8
    74  	flagMethod      flag = 1 << 9
    75  	flagMethodShift      = 10
    76  	flagRO          flag = flagStickyRO | flagEmbedRO
    77  )
    78  
    79  func (f flag) kind() Kind {
    80  	return Kind(f & flagKindMask)
    81  }
    82  
    83  // pointer returns the underlying pointer represented by v.
    84  // v.Kind() must be Ptr, Map, Chan, Func, or UnsafePointer
    85  func (v Value) pointer() unsafe.Pointer {
    86  	if v.typ.size != ptrSize || !v.typ.pointers() {
    87  		panic("can't call pointer on a non-pointer Value")
    88  	}
    89  	if v.flag&flagIndir != 0 {
    90  		return *(*unsafe.Pointer)(v.ptr)
    91  	}
    92  	return v.ptr
    93  }
    94  
    95  // packEface converts v to the empty interface.
    96  func packEface(v Value) interface{} {
    97  	t := v.typ
    98  	var i interface{}
    99  	e := (*emptyInterface)(unsafe.Pointer(&i))
   100  	// First, fill in the data portion of the interface.
   101  	switch {
   102  	case ifaceIndir(t):
   103  		if v.flag&flagIndir == 0 {
   104  			panic("bad indir")
   105  		}
   106  		// Value is indirect, and so is the interface we're making.
   107  		ptr := v.ptr
   108  		if v.flag&flagAddr != 0 {
   109  			// TODO: pass safe boolean from valueInterface so
   110  			// we don't need to copy if safe==true?
   111  			c := unsafe_New(t)
   112  			typedmemmove(t, c, ptr)
   113  			ptr = c
   114  		}
   115  		e.word = ptr
   116  	case v.flag&flagIndir != 0:
   117  		// Value is indirect, but interface is direct. We need
   118  		// to load the data at v.ptr into the interface data word.
   119  		e.word = *(*unsafe.Pointer)(v.ptr)
   120  	default:
   121  		// Value is direct, and so is the interface.
   122  		e.word = v.ptr
   123  	}
   124  	// Now, fill in the type portion. We're very careful here not
   125  	// to have any operation between the e.word and e.typ assignments
   126  	// that would let the garbage collector observe the partially-built
   127  	// interface value.
   128  	e.typ = t
   129  	return i
   130  }
   131  
   132  // unpackEface converts the empty interface i to a Value.
   133  func unpackEface(i interface{}) Value {
   134  	e := (*emptyInterface)(unsafe.Pointer(&i))
   135  	// NOTE: don't read e.word until we know whether it is really a pointer or not.
   136  	t := e.typ
   137  	if t == nil {
   138  		return Value{}
   139  	}
   140  	f := flag(t.Kind())
   141  	if ifaceIndir(t) {
   142  		f |= flagIndir
   143  	}
   144  	return Value{t, e.word, f}
   145  }
   146  
   147  // A ValueError occurs when a Value method is invoked on
   148  // a Value that does not support it. Such cases are documented
   149  // in the description of each method.
   150  type ValueError struct {
   151  	Method string
   152  	Kind   Kind
   153  }
   154  
   155  func (e *ValueError) Error() string {
   156  	if e.Kind == 0 {
   157  		return "reflect: call of " + e.Method + " on zero Value"
   158  	}
   159  	return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value"
   160  }
   161  
   162  // methodName returns the name of the calling method,
   163  // assumed to be two stack frames above.
   164  func methodName() string {
   165  	pc, _, _, _ := runtime.Caller(2)
   166  	f := runtime.FuncForPC(pc)
   167  	if f == nil {
   168  		return "unknown method"
   169  	}
   170  	return f.Name()
   171  }
   172  
   173  // emptyInterface is the header for an interface{} value.
   174  type emptyInterface struct {
   175  	typ  *rtype
   176  	word unsafe.Pointer
   177  }
   178  
   179  // nonEmptyInterface is the header for a interface value with methods.
   180  type nonEmptyInterface struct {
   181  	// see ../runtime/iface.go:/Itab
   182  	itab *struct {
   183  		ityp   *rtype // static interface type
   184  		typ    *rtype // dynamic concrete type
   185  		link   unsafe.Pointer
   186  		bad    int32
   187  		unused int32
   188  		fun    [100000]unsafe.Pointer // method table
   189  	}
   190  	word unsafe.Pointer
   191  }
   192  
   193  // mustBe panics if f's kind is not expected.
   194  // Making this a method on flag instead of on Value
   195  // (and embedding flag in Value) means that we can write
   196  // the very clear v.mustBe(Bool) and have it compile into
   197  // v.flag.mustBe(Bool), which will only bother to copy the
   198  // single important word for the receiver.
   199  func (f flag) mustBe(expected Kind) {
   200  	if f.kind() != expected {
   201  		panic(&ValueError{methodName(), f.kind()})
   202  	}
   203  }
   204  
   205  // mustBeExported panics if f records that the value was obtained using
   206  // an unexported field.
   207  func (f flag) mustBeExported() {
   208  	if f == 0 {
   209  		panic(&ValueError{methodName(), 0})
   210  	}
   211  	if f&flagRO != 0 {
   212  		panic("reflect: " + methodName() + " using value obtained using unexported field")
   213  	}
   214  }
   215  
   216  // mustBeAssignable panics if f records that the value is not assignable,
   217  // which is to say that either it was obtained using an unexported field
   218  // or it is not addressable.
   219  func (f flag) mustBeAssignable() {
   220  	if f == 0 {
   221  		panic(&ValueError{methodName(), Invalid})
   222  	}
   223  	// Assignable if addressable and not read-only.
   224  	if f&flagRO != 0 {
   225  		panic("reflect: " + methodName() + " using value obtained using unexported field")
   226  	}
   227  	if f&flagAddr == 0 {
   228  		panic("reflect: " + methodName() + " using unaddressable value")
   229  	}
   230  }
   231  
   232  // Addr returns a pointer value representing the address of v.
   233  // It panics if CanAddr() returns false.
   234  // Addr is typically used to obtain a pointer to a struct field
   235  // or slice element in order to call a method that requires a
   236  // pointer receiver.
   237  func (v Value) Addr() Value {
   238  	if v.flag&flagAddr == 0 {
   239  		panic("reflect.Value.Addr of unaddressable value")
   240  	}
   241  	return Value{v.typ.ptrTo(), v.ptr, (v.flag & flagRO) | flag(Ptr)}
   242  }
   243  
   244  // Bool returns v's underlying value.
   245  // It panics if v's kind is not Bool.
   246  func (v Value) Bool() bool {
   247  	v.mustBe(Bool)
   248  	return *(*bool)(v.ptr)
   249  }
   250  
   251  // Bytes returns v's underlying value.
   252  // It panics if v's underlying value is not a slice of bytes.
   253  func (v Value) Bytes() []byte {
   254  	v.mustBe(Slice)
   255  	if v.typ.Elem().Kind() != Uint8 {
   256  		panic("reflect.Value.Bytes of non-byte slice")
   257  	}
   258  	// Slice is always bigger than a word; assume flagIndir.
   259  	return *(*[]byte)(v.ptr)
   260  }
   261  
   262  // runes returns v's underlying value.
   263  // It panics if v's underlying value is not a slice of runes (int32s).
   264  func (v Value) runes() []rune {
   265  	v.mustBe(Slice)
   266  	if v.typ.Elem().Kind() != Int32 {
   267  		panic("reflect.Value.Bytes of non-rune slice")
   268  	}
   269  	// Slice is always bigger than a word; assume flagIndir.
   270  	return *(*[]rune)(v.ptr)
   271  }
   272  
   273  // CanAddr reports whether the value's address can be obtained with Addr.
   274  // Such values are called addressable. A value is addressable if it is
   275  // an element of a slice, an element of an addressable array,
   276  // a field of an addressable struct, or the result of dereferencing a pointer.
   277  // If CanAddr returns false, calling Addr will panic.
   278  func (v Value) CanAddr() bool {
   279  	return v.flag&flagAddr != 0
   280  }
   281  
   282  // CanSet reports whether the value of v can be changed.
   283  // A Value can be changed only if it is addressable and was not
   284  // obtained by the use of unexported struct fields.
   285  // If CanSet returns false, calling Set or any type-specific
   286  // setter (e.g., SetBool, SetInt) will panic.
   287  func (v Value) CanSet() bool {
   288  	return v.flag&(flagAddr|flagRO) == flagAddr
   289  }
   290  
   291  // Call calls the function v with the input arguments in.
   292  // For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]).
   293  // Call panics if v's Kind is not Func.
   294  // It returns the output results as Values.
   295  // As in Go, each input argument must be assignable to the
   296  // type of the function's corresponding input parameter.
   297  // If v is a variadic function, Call creates the variadic slice parameter
   298  // itself, copying in the corresponding values.
   299  func (v Value) Call(in []Value) []Value {
   300  	v.mustBe(Func)
   301  	v.mustBeExported()
   302  	return v.call("Call", in)
   303  }
   304  
   305  // CallSlice calls the variadic function v with the input arguments in,
   306  // assigning the slice in[len(in)-1] to v's final variadic argument.
   307  // For example, if len(in) == 3, v.CallSlice(in) represents the Go call v(in[0], in[1], in[2]...).
   308  // CallSlice panics if v's Kind is not Func or if v is not variadic.
   309  // It returns the output results as Values.
   310  // As in Go, each input argument must be assignable to the
   311  // type of the function's corresponding input parameter.
   312  func (v Value) CallSlice(in []Value) []Value {
   313  	v.mustBe(Func)
   314  	v.mustBeExported()
   315  	return v.call("CallSlice", in)
   316  }
   317  
   318  var callGC bool // for testing; see TestCallMethodJump
   319  
   320  func (v Value) call(op string, in []Value) []Value {
   321  	// Get function pointer, type.
   322  	t := v.typ
   323  	var (
   324  		fn       unsafe.Pointer
   325  		rcvr     Value
   326  		rcvrtype *rtype
   327  	)
   328  	if v.flag&flagMethod != 0 {
   329  		rcvr = v
   330  		rcvrtype, t, fn = methodReceiver(op, v, int(v.flag)>>flagMethodShift)
   331  	} else if v.flag&flagIndir != 0 {
   332  		fn = *(*unsafe.Pointer)(v.ptr)
   333  	} else {
   334  		fn = v.ptr
   335  	}
   336  
   337  	if fn == nil {
   338  		panic("reflect.Value.Call: call of nil function")
   339  	}
   340  
   341  	isSlice := op == "CallSlice"
   342  	n := t.NumIn()
   343  	if isSlice {
   344  		if !t.IsVariadic() {
   345  			panic("reflect: CallSlice of non-variadic function")
   346  		}
   347  		if len(in) < n {
   348  			panic("reflect: CallSlice with too few input arguments")
   349  		}
   350  		if len(in) > n {
   351  			panic("reflect: CallSlice with too many input arguments")
   352  		}
   353  	} else {
   354  		if t.IsVariadic() {
   355  			n--
   356  		}
   357  		if len(in) < n {
   358  			panic("reflect: Call with too few input arguments")
   359  		}
   360  		if !t.IsVariadic() && len(in) > n {
   361  			panic("reflect: Call with too many input arguments")
   362  		}
   363  	}
   364  	for _, x := range in {
   365  		if x.Kind() == Invalid {
   366  			panic("reflect: " + op + " using zero Value argument")
   367  		}
   368  	}
   369  	for i := 0; i < n; i++ {
   370  		if xt, targ := in[i].Type(), t.In(i); !xt.AssignableTo(targ) {
   371  			panic("reflect: " + op + " using " + xt.String() + " as type " + targ.String())
   372  		}
   373  	}
   374  	if !isSlice && t.IsVariadic() {
   375  		// prepare slice for remaining values
   376  		m := len(in) - n
   377  		slice := MakeSlice(t.In(n), m, m)
   378  		elem := t.In(n).Elem()
   379  		for i := 0; i < m; i++ {
   380  			x := in[n+i]
   381  			if xt := x.Type(); !xt.AssignableTo(elem) {
   382  				panic("reflect: cannot use " + xt.String() + " as type " + elem.String() + " in " + op)
   383  			}
   384  			slice.Index(i).Set(x)
   385  		}
   386  		origIn := in
   387  		in = make([]Value, n+1)
   388  		copy(in[:n], origIn)
   389  		in[n] = slice
   390  	}
   391  
   392  	nin := len(in)
   393  	if nin != t.NumIn() {
   394  		panic("reflect.Value.Call: wrong argument count")
   395  	}
   396  	nout := t.NumOut()
   397  
   398  	// Compute frame type.
   399  	frametype, _, retOffset, _, framePool := funcLayout(t, rcvrtype)
   400  
   401  	// Allocate a chunk of memory for frame.
   402  	var args unsafe.Pointer
   403  	if nout == 0 {
   404  		args = framePool.Get().(unsafe.Pointer)
   405  	} else {
   406  		// Can't use pool if the function has return values.
   407  		// We will leak pointer to args in ret, so its lifetime is not scoped.
   408  		args = unsafe_New(frametype)
   409  	}
   410  	off := uintptr(0)
   411  
   412  	// Copy inputs into args.
   413  	if rcvrtype != nil {
   414  		storeRcvr(rcvr, args)
   415  		off = ptrSize
   416  	}
   417  	for i, v := range in {
   418  		v.mustBeExported()
   419  		targ := t.In(i).(*rtype)
   420  		a := uintptr(targ.align)
   421  		off = (off + a - 1) &^ (a - 1)
   422  		n := targ.size
   423  		addr := unsafe.Pointer(uintptr(args) + off)
   424  		v = v.assignTo("reflect.Value.Call", targ, addr)
   425  		if v.flag&flagIndir != 0 {
   426  			typedmemmove(targ, addr, v.ptr)
   427  		} else {
   428  			*(*unsafe.Pointer)(addr) = v.ptr
   429  		}
   430  		off += n
   431  	}
   432  
   433  	// Call.
   434  	call(frametype, fn, args, uint32(frametype.size), uint32(retOffset))
   435  
   436  	// For testing; see TestCallMethodJump.
   437  	if callGC {
   438  		runtime.GC()
   439  	}
   440  
   441  	var ret []Value
   442  	if nout == 0 {
   443  		// This is untyped because the frame is really a
   444  		// stack, even though it's a heap object.
   445  		memclrNoHeapPointers(args, frametype.size)
   446  		framePool.Put(args)
   447  	} else {
   448  		// Zero the now unused input area of args,
   449  		// because the Values returned by this function contain pointers to the args object,
   450  		// and will thus keep the args object alive indefinitely.
   451  		memclrNoHeapPointers(args, retOffset)
   452  		// Wrap Values around return values in args.
   453  		ret = make([]Value, nout)
   454  		off = retOffset
   455  		for i := 0; i < nout; i++ {
   456  			tv := t.Out(i)
   457  			a := uintptr(tv.Align())
   458  			off = (off + a - 1) &^ (a - 1)
   459  			fl := flagIndir | flag(tv.Kind())
   460  			ret[i] = Value{tv.common(), unsafe.Pointer(uintptr(args) + off), fl}
   461  			off += tv.Size()
   462  		}
   463  	}
   464  
   465  	return ret
   466  }
   467  
   468  // callReflect is the call implementation used by a function
   469  // returned by MakeFunc. In many ways it is the opposite of the
   470  // method Value.call above. The method above converts a call using Values
   471  // into a call of a function with a concrete argument frame, while
   472  // callReflect converts a call of a function with a concrete argument
   473  // frame into a call using Values.
   474  // It is in this file so that it can be next to the call method above.
   475  // The remainder of the MakeFunc implementation is in makefunc.go.
   476  //
   477  // NOTE: This function must be marked as a "wrapper" in the generated code,
   478  // so that the linker can make it work correctly for panic and recover.
   479  // The gc compilers know to do that for the name "reflect.callReflect".
   480  func callReflect(ctxt *makeFuncImpl, frame unsafe.Pointer) {
   481  	ftyp := ctxt.typ
   482  	f := ctxt.fn
   483  
   484  	// Copy argument frame into Values.
   485  	ptr := frame
   486  	off := uintptr(0)
   487  	in := make([]Value, 0, int(ftyp.inCount))
   488  	for _, typ := range ftyp.in() {
   489  		off += -off & uintptr(typ.align-1)
   490  		addr := unsafe.Pointer(uintptr(ptr) + off)
   491  		v := Value{typ, nil, flag(typ.Kind())}
   492  		if ifaceIndir(typ) {
   493  			// value cannot be inlined in interface data.
   494  			// Must make a copy, because f might keep a reference to it,
   495  			// and we cannot let f keep a reference to the stack frame
   496  			// after this function returns, not even a read-only reference.
   497  			v.ptr = unsafe_New(typ)
   498  			typedmemmove(typ, v.ptr, addr)
   499  			v.flag |= flagIndir
   500  		} else {
   501  			v.ptr = *(*unsafe.Pointer)(addr)
   502  		}
   503  		in = append(in, v)
   504  		off += typ.size
   505  	}
   506  
   507  	// Call underlying function.
   508  	out := f(in)
   509  	numOut := ftyp.NumOut()
   510  	if len(out) != numOut {
   511  		panic("reflect: wrong return count from function created by MakeFunc")
   512  	}
   513  
   514  	// Copy results back into argument frame.
   515  	if numOut > 0 {
   516  		off += -off & (ptrSize - 1)
   517  		if runtime.GOARCH == "amd64p32" {
   518  			off = align(off, 8)
   519  		}
   520  		for i, typ := range ftyp.out() {
   521  			v := out[i]
   522  			if v.typ != typ {
   523  				panic("reflect: function created by MakeFunc using " + funcName(f) +
   524  					" returned wrong type: have " +
   525  					out[i].typ.String() + " for " + typ.String())
   526  			}
   527  			if v.flag&flagRO != 0 {
   528  				panic("reflect: function created by MakeFunc using " + funcName(f) +
   529  					" returned value obtained from unexported field")
   530  			}
   531  			off += -off & uintptr(typ.align-1)
   532  			addr := unsafe.Pointer(uintptr(ptr) + off)
   533  			if v.flag&flagIndir != 0 {
   534  				typedmemmove(typ, addr, v.ptr)
   535  			} else {
   536  				*(*unsafe.Pointer)(addr) = v.ptr
   537  			}
   538  			off += typ.size
   539  		}
   540  	}
   541  
   542  	// runtime.getArgInfo expects to be able to find ctxt on the
   543  	// stack when it finds our caller, makeFuncStub. Make sure it
   544  	// doesn't get garbage collected.
   545  	runtime.KeepAlive(ctxt)
   546  }
   547  
   548  // methodReceiver returns information about the receiver
   549  // described by v. The Value v may or may not have the
   550  // flagMethod bit set, so the kind cached in v.flag should
   551  // not be used.
   552  // The return value rcvrtype gives the method's actual receiver type.
   553  // The return value t gives the method type signature (without the receiver).
   554  // The return value fn is a pointer to the method code.
   555  func methodReceiver(op string, v Value, methodIndex int) (rcvrtype, t *rtype, fn unsafe.Pointer) {
   556  	i := methodIndex
   557  	if v.typ.Kind() == Interface {
   558  		tt := (*interfaceType)(unsafe.Pointer(v.typ))
   559  		if uint(i) >= uint(len(tt.methods)) {
   560  			panic("reflect: internal error: invalid method index")
   561  		}
   562  		m := &tt.methods[i]
   563  		if !tt.nameOff(m.name).isExported() {
   564  			panic("reflect: " + op + " of unexported method")
   565  		}
   566  		iface := (*nonEmptyInterface)(v.ptr)
   567  		if iface.itab == nil {
   568  			panic("reflect: " + op + " of method on nil interface value")
   569  		}
   570  		rcvrtype = iface.itab.typ
   571  		fn = unsafe.Pointer(&iface.itab.fun[i])
   572  		t = tt.typeOff(m.typ)
   573  	} else {
   574  		rcvrtype = v.typ
   575  		ut := v.typ.uncommon()
   576  		if ut == nil || uint(i) >= uint(ut.mcount) {
   577  			panic("reflect: internal error: invalid method index")
   578  		}
   579  		m := ut.methods()[i]
   580  		if !v.typ.nameOff(m.name).isExported() {
   581  			panic("reflect: " + op + " of unexported method")
   582  		}
   583  		ifn := v.typ.textOff(m.ifn)
   584  		fn = unsafe.Pointer(&ifn)
   585  		t = v.typ.typeOff(m.mtyp)
   586  	}
   587  	return
   588  }
   589  
   590  // v is a method receiver. Store at p the word which is used to
   591  // encode that receiver at the start of the argument list.
   592  // Reflect uses the "interface" calling convention for
   593  // methods, which always uses one word to record the receiver.
   594  func storeRcvr(v Value, p unsafe.Pointer) {
   595  	t := v.typ
   596  	if t.Kind() == Interface {
   597  		// the interface data word becomes the receiver word
   598  		iface := (*nonEmptyInterface)(v.ptr)
   599  		*(*unsafe.Pointer)(p) = iface.word
   600  	} else if v.flag&flagIndir != 0 && !ifaceIndir(t) {
   601  		*(*unsafe.Pointer)(p) = *(*unsafe.Pointer)(v.ptr)
   602  	} else {
   603  		*(*unsafe.Pointer)(p) = v.ptr
   604  	}
   605  }
   606  
   607  // align returns the result of rounding x up to a multiple of n.
   608  // n must be a power of two.
   609  func align(x, n uintptr) uintptr {
   610  	return (x + n - 1) &^ (n - 1)
   611  }
   612  
   613  // callMethod is the call implementation used by a function returned
   614  // by makeMethodValue (used by v.Method(i).Interface()).
   615  // It is a streamlined version of the usual reflect call: the caller has
   616  // already laid out the argument frame for us, so we don't have
   617  // to deal with individual Values for each argument.
   618  // It is in this file so that it can be next to the two similar functions above.
   619  // The remainder of the makeMethodValue implementation is in makefunc.go.
   620  //
   621  // NOTE: This function must be marked as a "wrapper" in the generated code,
   622  // so that the linker can make it work correctly for panic and recover.
   623  // The gc compilers know to do that for the name "reflect.callMethod".
   624  func callMethod(ctxt *methodValue, frame unsafe.Pointer) {
   625  	rcvr := ctxt.rcvr
   626  	rcvrtype, t, fn := methodReceiver("call", rcvr, ctxt.method)
   627  	frametype, argSize, retOffset, _, framePool := funcLayout(t, rcvrtype)
   628  
   629  	// Make a new frame that is one word bigger so we can store the receiver.
   630  	args := framePool.Get().(unsafe.Pointer)
   631  
   632  	// Copy in receiver and rest of args.
   633  	// Avoid constructing out-of-bounds pointers if there are no args.
   634  	storeRcvr(rcvr, args)
   635  	if argSize-ptrSize > 0 {
   636  		typedmemmovepartial(frametype, unsafe.Pointer(uintptr(args)+ptrSize), frame, ptrSize, argSize-ptrSize)
   637  	}
   638  
   639  	// Call.
   640  	call(frametype, fn, args, uint32(frametype.size), uint32(retOffset))
   641  
   642  	// Copy return values. On amd64p32, the beginning of return values
   643  	// is 64-bit aligned, so the caller's frame layout (which doesn't have
   644  	// a receiver) is different from the layout of the fn call, which has
   645  	// a receiver.
   646  	// Ignore any changes to args and just copy return values.
   647  	// Avoid constructing out-of-bounds pointers if there are no return values.
   648  	if frametype.size-retOffset > 0 {
   649  		callerRetOffset := retOffset - ptrSize
   650  		if runtime.GOARCH == "amd64p32" {
   651  			callerRetOffset = align(argSize-ptrSize, 8)
   652  		}
   653  		typedmemmovepartial(frametype,
   654  			unsafe.Pointer(uintptr(frame)+callerRetOffset),
   655  			unsafe.Pointer(uintptr(args)+retOffset),
   656  			retOffset,
   657  			frametype.size-retOffset)
   658  	}
   659  
   660  	// This is untyped because the frame is really a stack, even
   661  	// though it's a heap object.
   662  	memclrNoHeapPointers(args, frametype.size)
   663  	framePool.Put(args)
   664  
   665  	// See the comment in callReflect.
   666  	runtime.KeepAlive(ctxt)
   667  }
   668  
   669  // funcName returns the name of f, for use in error messages.
   670  func funcName(f func([]Value) []Value) string {
   671  	pc := *(*uintptr)(unsafe.Pointer(&f))
   672  	rf := runtime.FuncForPC(pc)
   673  	if rf != nil {
   674  		return rf.Name()
   675  	}
   676  	return "closure"
   677  }
   678  
   679  // Cap returns v's capacity.
   680  // It panics if v's Kind is not Array, Chan, or Slice.
   681  func (v Value) Cap() int {
   682  	k := v.kind()
   683  	switch k {
   684  	case Array:
   685  		return v.typ.Len()
   686  	case Chan:
   687  		return chancap(v.pointer())
   688  	case Slice:
   689  		// Slice is always bigger than a word; assume flagIndir.
   690  		return (*sliceHeader)(v.ptr).Cap
   691  	}
   692  	panic(&ValueError{"reflect.Value.Cap", v.kind()})
   693  }
   694  
   695  // Close closes the channel v.
   696  // It panics if v's Kind is not Chan.
   697  func (v Value) Close() {
   698  	v.mustBe(Chan)
   699  	v.mustBeExported()
   700  	chanclose(v.pointer())
   701  }
   702  
   703  // Complex returns v's underlying value, as a complex128.
   704  // It panics if v's Kind is not Complex64 or Complex128
   705  func (v Value) Complex() complex128 {
   706  	k := v.kind()
   707  	switch k {
   708  	case Complex64:
   709  		return complex128(*(*complex64)(v.ptr))
   710  	case Complex128:
   711  		return *(*complex128)(v.ptr)
   712  	}
   713  	panic(&ValueError{"reflect.Value.Complex", v.kind()})
   714  }
   715  
   716  // Elem returns the value that the interface v contains
   717  // or that the pointer v points to.
   718  // It panics if v's Kind is not Interface or Ptr.
   719  // It returns the zero Value if v is nil.
   720  func (v Value) Elem() Value {
   721  	k := v.kind()
   722  	switch k {
   723  	case Interface:
   724  		var eface interface{}
   725  		if v.typ.NumMethod() == 0 {
   726  			eface = *(*interface{})(v.ptr)
   727  		} else {
   728  			eface = (interface{})(*(*interface {
   729  				M()
   730  			})(v.ptr))
   731  		}
   732  		x := unpackEface(eface)
   733  		if x.flag != 0 {
   734  			x.flag |= v.flag & flagRO
   735  		}
   736  		return x
   737  	case Ptr:
   738  		ptr := v.ptr
   739  		if v.flag&flagIndir != 0 {
   740  			ptr = *(*unsafe.Pointer)(ptr)
   741  		}
   742  		// The returned value's address is v's value.
   743  		if ptr == nil {
   744  			return Value{}
   745  		}
   746  		tt := (*ptrType)(unsafe.Pointer(v.typ))
   747  		typ := tt.elem
   748  		fl := v.flag&flagRO | flagIndir | flagAddr
   749  		fl |= flag(typ.Kind())
   750  		return Value{typ, ptr, fl}
   751  	}
   752  	panic(&ValueError{"reflect.Value.Elem", v.kind()})
   753  }
   754  
   755  // Field returns the i'th field of the struct v.
   756  // It panics if v's Kind is not Struct or i is out of range.
   757  func (v Value) Field(i int) Value {
   758  	if v.kind() != Struct {
   759  		panic(&ValueError{"reflect.Value.Field", v.kind()})
   760  	}
   761  	tt := (*structType)(unsafe.Pointer(v.typ))
   762  	if uint(i) >= uint(len(tt.fields)) {
   763  		panic("reflect: Field index out of range")
   764  	}
   765  	field := &tt.fields[i]
   766  	typ := field.typ
   767  
   768  	// Inherit permission bits from v, but clear flagEmbedRO.
   769  	fl := v.flag&(flagStickyRO|flagIndir|flagAddr) | flag(typ.Kind())
   770  	// Using an unexported field forces flagRO.
   771  	if !field.name.isExported() {
   772  		if field.anon() {
   773  			fl |= flagEmbedRO
   774  		} else {
   775  			fl |= flagStickyRO
   776  		}
   777  	}
   778  	// Either flagIndir is set and v.ptr points at struct,
   779  	// or flagIndir is not set and v.ptr is the actual struct data.
   780  	// In the former case, we want v.ptr + offset.
   781  	// In the latter case, we must have field.offset = 0,
   782  	// so v.ptr + field.offset is still okay.
   783  	ptr := unsafe.Pointer(uintptr(v.ptr) + field.offset())
   784  	return Value{typ, ptr, fl}
   785  }
   786  
   787  // FieldByIndex returns the nested field corresponding to index.
   788  // It panics if v's Kind is not struct.
   789  func (v Value) FieldByIndex(index []int) Value {
   790  	if len(index) == 1 {
   791  		return v.Field(index[0])
   792  	}
   793  	v.mustBe(Struct)
   794  	for i, x := range index {
   795  		if i > 0 {
   796  			if v.Kind() == Ptr && v.typ.Elem().Kind() == Struct {
   797  				if v.IsNil() {
   798  					panic("reflect: indirection through nil pointer to embedded struct")
   799  				}
   800  				v = v.Elem()
   801  			}
   802  		}
   803  		v = v.Field(x)
   804  	}
   805  	return v
   806  }
   807  
   808  // FieldByName returns the struct field with the given name.
   809  // It returns the zero Value if no field was found.
   810  // It panics if v's Kind is not struct.
   811  func (v Value) FieldByName(name string) Value {
   812  	v.mustBe(Struct)
   813  	if f, ok := v.typ.FieldByName(name); ok {
   814  		return v.FieldByIndex(f.Index)
   815  	}
   816  	return Value{}
   817  }
   818  
   819  // FieldByNameFunc returns the struct field with a name
   820  // that satisfies the match function.
   821  // It panics if v's Kind is not struct.
   822  // It returns the zero Value if no field was found.
   823  func (v Value) FieldByNameFunc(match func(string) bool) Value {
   824  	if f, ok := v.typ.FieldByNameFunc(match); ok {
   825  		return v.FieldByIndex(f.Index)
   826  	}
   827  	return Value{}
   828  }
   829  
   830  // Float returns v's underlying value, as a float64.
   831  // It panics if v's Kind is not Float32 or Float64
   832  func (v Value) Float() float64 {
   833  	k := v.kind()
   834  	switch k {
   835  	case Float32:
   836  		return float64(*(*float32)(v.ptr))
   837  	case Float64:
   838  		return *(*float64)(v.ptr)
   839  	}
   840  	panic(&ValueError{"reflect.Value.Float", v.kind()})
   841  }
   842  
   843  var uint8Type = TypeOf(uint8(0)).(*rtype)
   844  
   845  // Index returns v's i'th element.
   846  // It panics if v's Kind is not Array, Slice, or String or i is out of range.
   847  func (v Value) Index(i int) Value {
   848  	switch v.kind() {
   849  	case Array:
   850  		tt := (*arrayType)(unsafe.Pointer(v.typ))
   851  		if uint(i) >= uint(tt.len) {
   852  			panic("reflect: array index out of range")
   853  		}
   854  		typ := tt.elem
   855  		offset := uintptr(i) * typ.size
   856  
   857  		// Either flagIndir is set and v.ptr points at array,
   858  		// or flagIndir is not set and v.ptr is the actual array data.
   859  		// In the former case, we want v.ptr + offset.
   860  		// In the latter case, we must be doing Index(0), so offset = 0,
   861  		// so v.ptr + offset is still okay.
   862  		val := unsafe.Pointer(uintptr(v.ptr) + offset)
   863  		fl := v.flag&(flagRO|flagIndir|flagAddr) | flag(typ.Kind()) // bits same as overall array
   864  		return Value{typ, val, fl}
   865  
   866  	case Slice:
   867  		// Element flag same as Elem of Ptr.
   868  		// Addressable, indirect, possibly read-only.
   869  		s := (*sliceHeader)(v.ptr)
   870  		if uint(i) >= uint(s.Len) {
   871  			panic("reflect: slice index out of range")
   872  		}
   873  		tt := (*sliceType)(unsafe.Pointer(v.typ))
   874  		typ := tt.elem
   875  		val := arrayAt(s.Data, i, typ.size)
   876  		fl := flagAddr | flagIndir | v.flag&flagRO | flag(typ.Kind())
   877  		return Value{typ, val, fl}
   878  
   879  	case String:
   880  		s := (*stringHeader)(v.ptr)
   881  		if uint(i) >= uint(s.Len) {
   882  			panic("reflect: string index out of range")
   883  		}
   884  		p := arrayAt(s.Data, i, 1)
   885  		fl := v.flag&flagRO | flag(Uint8) | flagIndir
   886  		return Value{uint8Type, p, fl}
   887  	}
   888  	panic(&ValueError{"reflect.Value.Index", v.kind()})
   889  }
   890  
   891  // Int returns v's underlying value, as an int64.
   892  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.
   893  func (v Value) Int() int64 {
   894  	k := v.kind()
   895  	p := v.ptr
   896  	switch k {
   897  	case Int:
   898  		return int64(*(*int)(p))
   899  	case Int8:
   900  		return int64(*(*int8)(p))
   901  	case Int16:
   902  		return int64(*(*int16)(p))
   903  	case Int32:
   904  		return int64(*(*int32)(p))
   905  	case Int64:
   906  		return *(*int64)(p)
   907  	}
   908  	panic(&ValueError{"reflect.Value.Int", v.kind()})
   909  }
   910  
   911  // CanInterface reports whether Interface can be used without panicking.
   912  func (v Value) CanInterface() bool {
   913  	if v.flag == 0 {
   914  		panic(&ValueError{"reflect.Value.CanInterface", Invalid})
   915  	}
   916  	return v.flag&flagRO == 0
   917  }
   918  
   919  // Interface returns v's current value as an interface{}.
   920  // It is equivalent to:
   921  //	var i interface{} = (v's underlying value)
   922  // It panics if the Value was obtained by accessing
   923  // unexported struct fields.
   924  func (v Value) Interface() (i interface{}) {
   925  	return valueInterface(v, true)
   926  }
   927  
   928  func valueInterface(v Value, safe bool) interface{} {
   929  	if v.flag == 0 {
   930  		panic(&ValueError{"reflect.Value.Interface", 0})
   931  	}
   932  	if safe && v.flag&flagRO != 0 {
   933  		// Do not allow access to unexported values via Interface,
   934  		// because they might be pointers that should not be
   935  		// writable or methods or function that should not be callable.
   936  		panic("reflect.Value.Interface: cannot return value obtained from unexported field or method")
   937  	}
   938  	if v.flag&flagMethod != 0 {
   939  		v = makeMethodValue("Interface", v)
   940  	}
   941  
   942  	if v.kind() == Interface {
   943  		// Special case: return the element inside the interface.
   944  		// Empty interface has one layout, all interfaces with
   945  		// methods have a second layout.
   946  		if v.NumMethod() == 0 {
   947  			return *(*interface{})(v.ptr)
   948  		}
   949  		return *(*interface {
   950  			M()
   951  		})(v.ptr)
   952  	}
   953  
   954  	// TODO: pass safe to packEface so we don't need to copy if safe==true?
   955  	return packEface(v)
   956  }
   957  
   958  // InterfaceData returns the interface v's value as a uintptr pair.
   959  // It panics if v's Kind is not Interface.
   960  func (v Value) InterfaceData() [2]uintptr {
   961  	// TODO: deprecate this
   962  	v.mustBe(Interface)
   963  	// We treat this as a read operation, so we allow
   964  	// it even for unexported data, because the caller
   965  	// has to import "unsafe" to turn it into something
   966  	// that can be abused.
   967  	// Interface value is always bigger than a word; assume flagIndir.
   968  	return *(*[2]uintptr)(v.ptr)
   969  }
   970  
   971  // IsNil reports whether its argument v is nil. The argument must be
   972  // a chan, func, interface, map, pointer, or slice value; if it is
   973  // not, IsNil panics. Note that IsNil is not always equivalent to a
   974  // regular comparison with nil in Go. For example, if v was created
   975  // by calling ValueOf with an uninitialized interface variable i,
   976  // i==nil will be true but v.IsNil will panic as v will be the zero
   977  // Value.
   978  func (v Value) IsNil() bool {
   979  	k := v.kind()
   980  	switch k {
   981  	case Chan, Func, Map, Ptr:
   982  		if v.flag&flagMethod != 0 {
   983  			return false
   984  		}
   985  		ptr := v.ptr
   986  		if v.flag&flagIndir != 0 {
   987  			ptr = *(*unsafe.Pointer)(ptr)
   988  		}
   989  		return ptr == nil
   990  	case Interface, Slice:
   991  		// Both interface and slice are nil if first word is 0.
   992  		// Both are always bigger than a word; assume flagIndir.
   993  		return *(*unsafe.Pointer)(v.ptr) == nil
   994  	}
   995  	panic(&ValueError{"reflect.Value.IsNil", v.kind()})
   996  }
   997  
   998  // IsValid reports whether v represents a value.
   999  // It returns false if v is the zero Value.
  1000  // If IsValid returns false, all other methods except String panic.
  1001  // Most functions and methods never return an invalid value.
  1002  // If one does, its documentation states the conditions explicitly.
  1003  func (v Value) IsValid() bool {
  1004  	return v.flag != 0
  1005  }
  1006  
  1007  // Kind returns v's Kind.
  1008  // If v is the zero Value (IsValid returns false), Kind returns Invalid.
  1009  func (v Value) Kind() Kind {
  1010  	return v.kind()
  1011  }
  1012  
  1013  // Len returns v's length.
  1014  // It panics if v's Kind is not Array, Chan, Map, Slice, or String.
  1015  func (v Value) Len() int {
  1016  	k := v.kind()
  1017  	switch k {
  1018  	case Array:
  1019  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1020  		return int(tt.len)
  1021  	case Chan:
  1022  		return chanlen(v.pointer())
  1023  	case Map:
  1024  		return maplen(v.pointer())
  1025  	case Slice:
  1026  		// Slice is bigger than a word; assume flagIndir.
  1027  		return (*sliceHeader)(v.ptr).Len
  1028  	case String:
  1029  		// String is bigger than a word; assume flagIndir.
  1030  		return (*stringHeader)(v.ptr).Len
  1031  	}
  1032  	panic(&ValueError{"reflect.Value.Len", v.kind()})
  1033  }
  1034  
  1035  // MapIndex returns the value associated with key in the map v.
  1036  // It panics if v's Kind is not Map.
  1037  // It returns the zero Value if key is not found in the map or if v represents a nil map.
  1038  // As in Go, the key's value must be assignable to the map's key type.
  1039  func (v Value) MapIndex(key Value) Value {
  1040  	v.mustBe(Map)
  1041  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1042  
  1043  	// Do not require key to be exported, so that DeepEqual
  1044  	// and other programs can use all the keys returned by
  1045  	// MapKeys as arguments to MapIndex. If either the map
  1046  	// or the key is unexported, though, the result will be
  1047  	// considered unexported. This is consistent with the
  1048  	// behavior for structs, which allow read but not write
  1049  	// of unexported fields.
  1050  	key = key.assignTo("reflect.Value.MapIndex", tt.key, nil)
  1051  
  1052  	var k unsafe.Pointer
  1053  	if key.flag&flagIndir != 0 {
  1054  		k = key.ptr
  1055  	} else {
  1056  		k = unsafe.Pointer(&key.ptr)
  1057  	}
  1058  	e := mapaccess(v.typ, v.pointer(), k)
  1059  	if e == nil {
  1060  		return Value{}
  1061  	}
  1062  	typ := tt.elem
  1063  	fl := (v.flag | key.flag) & flagRO
  1064  	fl |= flag(typ.Kind())
  1065  	if ifaceIndir(typ) {
  1066  		// Copy result so future changes to the map
  1067  		// won't change the underlying value.
  1068  		c := unsafe_New(typ)
  1069  		typedmemmove(typ, c, e)
  1070  		return Value{typ, c, fl | flagIndir}
  1071  	} else {
  1072  		return Value{typ, *(*unsafe.Pointer)(e), fl}
  1073  	}
  1074  }
  1075  
  1076  // MapKeys returns a slice containing all the keys present in the map,
  1077  // in unspecified order.
  1078  // It panics if v's Kind is not Map.
  1079  // It returns an empty slice if v represents a nil map.
  1080  func (v Value) MapKeys() []Value {
  1081  	v.mustBe(Map)
  1082  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1083  	keyType := tt.key
  1084  
  1085  	fl := v.flag&flagRO | flag(keyType.Kind())
  1086  
  1087  	m := v.pointer()
  1088  	mlen := int(0)
  1089  	if m != nil {
  1090  		mlen = maplen(m)
  1091  	}
  1092  	it := mapiterinit(v.typ, m)
  1093  	a := make([]Value, mlen)
  1094  	var i int
  1095  	for i = 0; i < len(a); i++ {
  1096  		key := mapiterkey(it)
  1097  		if key == nil {
  1098  			// Someone deleted an entry from the map since we
  1099  			// called maplen above. It's a data race, but nothing
  1100  			// we can do about it.
  1101  			break
  1102  		}
  1103  		if ifaceIndir(keyType) {
  1104  			// Copy result so future changes to the map
  1105  			// won't change the underlying value.
  1106  			c := unsafe_New(keyType)
  1107  			typedmemmove(keyType, c, key)
  1108  			a[i] = Value{keyType, c, fl | flagIndir}
  1109  		} else {
  1110  			a[i] = Value{keyType, *(*unsafe.Pointer)(key), fl}
  1111  		}
  1112  		mapiternext(it)
  1113  	}
  1114  	return a[:i]
  1115  }
  1116  
  1117  // Method returns a function value corresponding to v's i'th method.
  1118  // The arguments to a Call on the returned function should not include
  1119  // a receiver; the returned function will always use v as the receiver.
  1120  // Method panics if i is out of range or if v is a nil interface value.
  1121  func (v Value) Method(i int) Value {
  1122  	if v.typ == nil {
  1123  		panic(&ValueError{"reflect.Value.Method", Invalid})
  1124  	}
  1125  	if v.flag&flagMethod != 0 || uint(i) >= uint(v.typ.NumMethod()) {
  1126  		panic("reflect: Method index out of range")
  1127  	}
  1128  	if v.typ.Kind() == Interface && v.IsNil() {
  1129  		panic("reflect: Method on nil interface value")
  1130  	}
  1131  	fl := v.flag & (flagStickyRO | flagIndir) // Clear flagEmbedRO
  1132  	fl |= flag(Func)
  1133  	fl |= flag(i)<<flagMethodShift | flagMethod
  1134  	return Value{v.typ, v.ptr, fl}
  1135  }
  1136  
  1137  // NumMethod returns the number of methods in the value's method set.
  1138  func (v Value) NumMethod() int {
  1139  	if v.typ == nil {
  1140  		panic(&ValueError{"reflect.Value.NumMethod", Invalid})
  1141  	}
  1142  	if v.flag&flagMethod != 0 {
  1143  		return 0
  1144  	}
  1145  	return v.typ.NumMethod()
  1146  }
  1147  
  1148  // MethodByName returns a function value corresponding to the method
  1149  // of v with the given name.
  1150  // The arguments to a Call on the returned function should not include
  1151  // a receiver; the returned function will always use v as the receiver.
  1152  // It returns the zero Value if no method was found.
  1153  func (v Value) MethodByName(name string) Value {
  1154  	if v.typ == nil {
  1155  		panic(&ValueError{"reflect.Value.MethodByName", Invalid})
  1156  	}
  1157  	if v.flag&flagMethod != 0 {
  1158  		return Value{}
  1159  	}
  1160  	m, ok := v.typ.MethodByName(name)
  1161  	if !ok {
  1162  		return Value{}
  1163  	}
  1164  	return v.Method(m.Index)
  1165  }
  1166  
  1167  // NumField returns the number of fields in the struct v.
  1168  // It panics if v's Kind is not Struct.
  1169  func (v Value) NumField() int {
  1170  	v.mustBe(Struct)
  1171  	tt := (*structType)(unsafe.Pointer(v.typ))
  1172  	return len(tt.fields)
  1173  }
  1174  
  1175  // OverflowComplex reports whether the complex128 x cannot be represented by v's type.
  1176  // It panics if v's Kind is not Complex64 or Complex128.
  1177  func (v Value) OverflowComplex(x complex128) bool {
  1178  	k := v.kind()
  1179  	switch k {
  1180  	case Complex64:
  1181  		return overflowFloat32(real(x)) || overflowFloat32(imag(x))
  1182  	case Complex128:
  1183  		return false
  1184  	}
  1185  	panic(&ValueError{"reflect.Value.OverflowComplex", v.kind()})
  1186  }
  1187  
  1188  // OverflowFloat reports whether the float64 x cannot be represented by v's type.
  1189  // It panics if v's Kind is not Float32 or Float64.
  1190  func (v Value) OverflowFloat(x float64) bool {
  1191  	k := v.kind()
  1192  	switch k {
  1193  	case Float32:
  1194  		return overflowFloat32(x)
  1195  	case Float64:
  1196  		return false
  1197  	}
  1198  	panic(&ValueError{"reflect.Value.OverflowFloat", v.kind()})
  1199  }
  1200  
  1201  func overflowFloat32(x float64) bool {
  1202  	if x < 0 {
  1203  		x = -x
  1204  	}
  1205  	return math.MaxFloat32 < x && x <= math.MaxFloat64
  1206  }
  1207  
  1208  // OverflowInt reports whether the int64 x cannot be represented by v's type.
  1209  // It panics if v's Kind is not Int, Int8, int16, Int32, or Int64.
  1210  func (v Value) OverflowInt(x int64) bool {
  1211  	k := v.kind()
  1212  	switch k {
  1213  	case Int, Int8, Int16, Int32, Int64:
  1214  		bitSize := v.typ.size * 8
  1215  		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
  1216  		return x != trunc
  1217  	}
  1218  	panic(&ValueError{"reflect.Value.OverflowInt", v.kind()})
  1219  }
  1220  
  1221  // OverflowUint reports whether the uint64 x cannot be represented by v's type.
  1222  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
  1223  func (v Value) OverflowUint(x uint64) bool {
  1224  	k := v.kind()
  1225  	switch k {
  1226  	case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64:
  1227  		bitSize := v.typ.size * 8
  1228  		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
  1229  		return x != trunc
  1230  	}
  1231  	panic(&ValueError{"reflect.Value.OverflowUint", v.kind()})
  1232  }
  1233  
  1234  // Pointer returns v's value as a uintptr.
  1235  // It returns uintptr instead of unsafe.Pointer so that
  1236  // code using reflect cannot obtain unsafe.Pointers
  1237  // without importing the unsafe package explicitly.
  1238  // It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer.
  1239  //
  1240  // If v's Kind is Func, the returned pointer is an underlying
  1241  // code pointer, but not necessarily enough to identify a
  1242  // single function uniquely. The only guarantee is that the
  1243  // result is zero if and only if v is a nil func Value.
  1244  //
  1245  // If v's Kind is Slice, the returned pointer is to the first
  1246  // element of the slice. If the slice is nil the returned value
  1247  // is 0.  If the slice is empty but non-nil the return value is non-zero.
  1248  func (v Value) Pointer() uintptr {
  1249  	// TODO: deprecate
  1250  	k := v.kind()
  1251  	switch k {
  1252  	case Chan, Map, Ptr, UnsafePointer:
  1253  		return uintptr(v.pointer())
  1254  	case Func:
  1255  		if v.flag&flagMethod != 0 {
  1256  			// As the doc comment says, the returned pointer is an
  1257  			// underlying code pointer but not necessarily enough to
  1258  			// identify a single function uniquely. All method expressions
  1259  			// created via reflect have the same underlying code pointer,
  1260  			// so their Pointers are equal. The function used here must
  1261  			// match the one used in makeMethodValue.
  1262  			f := methodValueCall
  1263  			return **(**uintptr)(unsafe.Pointer(&f))
  1264  		}
  1265  		p := v.pointer()
  1266  		// Non-nil func value points at data block.
  1267  		// First word of data block is actual code.
  1268  		if p != nil {
  1269  			p = *(*unsafe.Pointer)(p)
  1270  		}
  1271  		return uintptr(p)
  1272  
  1273  	case Slice:
  1274  		return (*SliceHeader)(v.ptr).Data
  1275  	}
  1276  	panic(&ValueError{"reflect.Value.Pointer", v.kind()})
  1277  }
  1278  
  1279  // Recv receives and returns a value from the channel v.
  1280  // It panics if v's Kind is not Chan.
  1281  // The receive blocks until a value is ready.
  1282  // The boolean value ok is true if the value x corresponds to a send
  1283  // on the channel, false if it is a zero value received because the channel is closed.
  1284  func (v Value) Recv() (x Value, ok bool) {
  1285  	v.mustBe(Chan)
  1286  	v.mustBeExported()
  1287  	return v.recv(false)
  1288  }
  1289  
  1290  // internal recv, possibly non-blocking (nb).
  1291  // v is known to be a channel.
  1292  func (v Value) recv(nb bool) (val Value, ok bool) {
  1293  	tt := (*chanType)(unsafe.Pointer(v.typ))
  1294  	if ChanDir(tt.dir)&RecvDir == 0 {
  1295  		panic("reflect: recv on send-only channel")
  1296  	}
  1297  	t := tt.elem
  1298  	val = Value{t, nil, flag(t.Kind())}
  1299  	var p unsafe.Pointer
  1300  	if ifaceIndir(t) {
  1301  		p = unsafe_New(t)
  1302  		val.ptr = p
  1303  		val.flag |= flagIndir
  1304  	} else {
  1305  		p = unsafe.Pointer(&val.ptr)
  1306  	}
  1307  	selected, ok := chanrecv(v.pointer(), nb, p)
  1308  	if !selected {
  1309  		val = Value{}
  1310  	}
  1311  	return
  1312  }
  1313  
  1314  // Send sends x on the channel v.
  1315  // It panics if v's kind is not Chan or if x's type is not the same type as v's element type.
  1316  // As in Go, x's value must be assignable to the channel's element type.
  1317  func (v Value) Send(x Value) {
  1318  	v.mustBe(Chan)
  1319  	v.mustBeExported()
  1320  	v.send(x, false)
  1321  }
  1322  
  1323  // internal send, possibly non-blocking.
  1324  // v is known to be a channel.
  1325  func (v Value) send(x Value, nb bool) (selected bool) {
  1326  	tt := (*chanType)(unsafe.Pointer(v.typ))
  1327  	if ChanDir(tt.dir)&SendDir == 0 {
  1328  		panic("reflect: send on recv-only channel")
  1329  	}
  1330  	x.mustBeExported()
  1331  	x = x.assignTo("reflect.Value.Send", tt.elem, nil)
  1332  	var p unsafe.Pointer
  1333  	if x.flag&flagIndir != 0 {
  1334  		p = x.ptr
  1335  	} else {
  1336  		p = unsafe.Pointer(&x.ptr)
  1337  	}
  1338  	return chansend(v.pointer(), p, nb)
  1339  }
  1340  
  1341  // Set assigns x to the value v.
  1342  // It panics if CanSet returns false.
  1343  // As in Go, x's value must be assignable to v's type.
  1344  func (v Value) Set(x Value) {
  1345  	v.mustBeAssignable()
  1346  	x.mustBeExported() // do not let unexported x leak
  1347  	var target unsafe.Pointer
  1348  	if v.kind() == Interface {
  1349  		target = v.ptr
  1350  	}
  1351  	x = x.assignTo("reflect.Set", v.typ, target)
  1352  	if x.flag&flagIndir != 0 {
  1353  		typedmemmove(v.typ, v.ptr, x.ptr)
  1354  	} else {
  1355  		*(*unsafe.Pointer)(v.ptr) = x.ptr
  1356  	}
  1357  }
  1358  
  1359  // SetBool sets v's underlying value.
  1360  // It panics if v's Kind is not Bool or if CanSet() is false.
  1361  func (v Value) SetBool(x bool) {
  1362  	v.mustBeAssignable()
  1363  	v.mustBe(Bool)
  1364  	*(*bool)(v.ptr) = x
  1365  }
  1366  
  1367  // SetBytes sets v's underlying value.
  1368  // It panics if v's underlying value is not a slice of bytes.
  1369  func (v Value) SetBytes(x []byte) {
  1370  	v.mustBeAssignable()
  1371  	v.mustBe(Slice)
  1372  	if v.typ.Elem().Kind() != Uint8 {
  1373  		panic("reflect.Value.SetBytes of non-byte slice")
  1374  	}
  1375  	*(*[]byte)(v.ptr) = x
  1376  }
  1377  
  1378  // setRunes sets v's underlying value.
  1379  // It panics if v's underlying value is not a slice of runes (int32s).
  1380  func (v Value) setRunes(x []rune) {
  1381  	v.mustBeAssignable()
  1382  	v.mustBe(Slice)
  1383  	if v.typ.Elem().Kind() != Int32 {
  1384  		panic("reflect.Value.setRunes of non-rune slice")
  1385  	}
  1386  	*(*[]rune)(v.ptr) = x
  1387  }
  1388  
  1389  // SetComplex sets v's underlying value to x.
  1390  // It panics if v's Kind is not Complex64 or Complex128, or if CanSet() is false.
  1391  func (v Value) SetComplex(x complex128) {
  1392  	v.mustBeAssignable()
  1393  	switch k := v.kind(); k {
  1394  	default:
  1395  		panic(&ValueError{"reflect.Value.SetComplex", v.kind()})
  1396  	case Complex64:
  1397  		*(*complex64)(v.ptr) = complex64(x)
  1398  	case Complex128:
  1399  		*(*complex128)(v.ptr) = x
  1400  	}
  1401  }
  1402  
  1403  // SetFloat sets v's underlying value to x.
  1404  // It panics if v's Kind is not Float32 or Float64, or if CanSet() is false.
  1405  func (v Value) SetFloat(x float64) {
  1406  	v.mustBeAssignable()
  1407  	switch k := v.kind(); k {
  1408  	default:
  1409  		panic(&ValueError{"reflect.Value.SetFloat", v.kind()})
  1410  	case Float32:
  1411  		*(*float32)(v.ptr) = float32(x)
  1412  	case Float64:
  1413  		*(*float64)(v.ptr) = x
  1414  	}
  1415  }
  1416  
  1417  // SetInt sets v's underlying value to x.
  1418  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64, or if CanSet() is false.
  1419  func (v Value) SetInt(x int64) {
  1420  	v.mustBeAssignable()
  1421  	switch k := v.kind(); k {
  1422  	default:
  1423  		panic(&ValueError{"reflect.Value.SetInt", v.kind()})
  1424  	case Int:
  1425  		*(*int)(v.ptr) = int(x)
  1426  	case Int8:
  1427  		*(*int8)(v.ptr) = int8(x)
  1428  	case Int16:
  1429  		*(*int16)(v.ptr) = int16(x)
  1430  	case Int32:
  1431  		*(*int32)(v.ptr) = int32(x)
  1432  	case Int64:
  1433  		*(*int64)(v.ptr) = x
  1434  	}
  1435  }
  1436  
  1437  // SetLen sets v's length to n.
  1438  // It panics if v's Kind is not Slice or if n is negative or
  1439  // greater than the capacity of the slice.
  1440  func (v Value) SetLen(n int) {
  1441  	v.mustBeAssignable()
  1442  	v.mustBe(Slice)
  1443  	s := (*sliceHeader)(v.ptr)
  1444  	if uint(n) > uint(s.Cap) {
  1445  		panic("reflect: slice length out of range in SetLen")
  1446  	}
  1447  	s.Len = n
  1448  }
  1449  
  1450  // SetCap sets v's capacity to n.
  1451  // It panics if v's Kind is not Slice or if n is smaller than the length or
  1452  // greater than the capacity of the slice.
  1453  func (v Value) SetCap(n int) {
  1454  	v.mustBeAssignable()
  1455  	v.mustBe(Slice)
  1456  	s := (*sliceHeader)(v.ptr)
  1457  	if n < s.Len || n > s.Cap {
  1458  		panic("reflect: slice capacity out of range in SetCap")
  1459  	}
  1460  	s.Cap = n
  1461  }
  1462  
  1463  // SetMapIndex sets the value associated with key in the map v to val.
  1464  // It panics if v's Kind is not Map.
  1465  // If val is the zero Value, SetMapIndex deletes the key from the map.
  1466  // Otherwise if v holds a nil map, SetMapIndex will panic.
  1467  // As in Go, key's value must be assignable to the map's key type,
  1468  // and val's value must be assignable to the map's value type.
  1469  func (v Value) SetMapIndex(key, val Value) {
  1470  	v.mustBe(Map)
  1471  	v.mustBeExported()
  1472  	key.mustBeExported()
  1473  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1474  	key = key.assignTo("reflect.Value.SetMapIndex", tt.key, nil)
  1475  	var k unsafe.Pointer
  1476  	if key.flag&flagIndir != 0 {
  1477  		k = key.ptr
  1478  	} else {
  1479  		k = unsafe.Pointer(&key.ptr)
  1480  	}
  1481  	if val.typ == nil {
  1482  		mapdelete(v.typ, v.pointer(), k)
  1483  		return
  1484  	}
  1485  	val.mustBeExported()
  1486  	val = val.assignTo("reflect.Value.SetMapIndex", tt.elem, nil)
  1487  	var e unsafe.Pointer
  1488  	if val.flag&flagIndir != 0 {
  1489  		e = val.ptr
  1490  	} else {
  1491  		e = unsafe.Pointer(&val.ptr)
  1492  	}
  1493  	mapassign(v.typ, v.pointer(), k, e)
  1494  }
  1495  
  1496  // SetUint sets v's underlying value to x.
  1497  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64, or if CanSet() is false.
  1498  func (v Value) SetUint(x uint64) {
  1499  	v.mustBeAssignable()
  1500  	switch k := v.kind(); k {
  1501  	default:
  1502  		panic(&ValueError{"reflect.Value.SetUint", v.kind()})
  1503  	case Uint:
  1504  		*(*uint)(v.ptr) = uint(x)
  1505  	case Uint8:
  1506  		*(*uint8)(v.ptr) = uint8(x)
  1507  	case Uint16:
  1508  		*(*uint16)(v.ptr) = uint16(x)
  1509  	case Uint32:
  1510  		*(*uint32)(v.ptr) = uint32(x)
  1511  	case Uint64:
  1512  		*(*uint64)(v.ptr) = x
  1513  	case Uintptr:
  1514  		*(*uintptr)(v.ptr) = uintptr(x)
  1515  	}
  1516  }
  1517  
  1518  // SetPointer sets the unsafe.Pointer value v to x.
  1519  // It panics if v's Kind is not UnsafePointer.
  1520  func (v Value) SetPointer(x unsafe.Pointer) {
  1521  	v.mustBeAssignable()
  1522  	v.mustBe(UnsafePointer)
  1523  	*(*unsafe.Pointer)(v.ptr) = x
  1524  }
  1525  
  1526  // SetString sets v's underlying value to x.
  1527  // It panics if v's Kind is not String or if CanSet() is false.
  1528  func (v Value) SetString(x string) {
  1529  	v.mustBeAssignable()
  1530  	v.mustBe(String)
  1531  	*(*string)(v.ptr) = x
  1532  }
  1533  
  1534  // Slice returns v[i:j].
  1535  // It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array,
  1536  // or if the indexes are out of bounds.
  1537  func (v Value) Slice(i, j int) Value {
  1538  	var (
  1539  		cap  int
  1540  		typ  *sliceType
  1541  		base unsafe.Pointer
  1542  	)
  1543  	switch kind := v.kind(); kind {
  1544  	default:
  1545  		panic(&ValueError{"reflect.Value.Slice", v.kind()})
  1546  
  1547  	case Array:
  1548  		if v.flag&flagAddr == 0 {
  1549  			panic("reflect.Value.Slice: slice of unaddressable array")
  1550  		}
  1551  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1552  		cap = int(tt.len)
  1553  		typ = (*sliceType)(unsafe.Pointer(tt.slice))
  1554  		base = v.ptr
  1555  
  1556  	case Slice:
  1557  		typ = (*sliceType)(unsafe.Pointer(v.typ))
  1558  		s := (*sliceHeader)(v.ptr)
  1559  		base = s.Data
  1560  		cap = s.Cap
  1561  
  1562  	case String:
  1563  		s := (*stringHeader)(v.ptr)
  1564  		if i < 0 || j < i || j > s.Len {
  1565  			panic("reflect.Value.Slice: string slice index out of bounds")
  1566  		}
  1567  		t := stringHeader{arrayAt(s.Data, i, 1), j - i}
  1568  		return Value{v.typ, unsafe.Pointer(&t), v.flag}
  1569  	}
  1570  
  1571  	if i < 0 || j < i || j > cap {
  1572  		panic("reflect.Value.Slice: slice index out of bounds")
  1573  	}
  1574  
  1575  	// Declare slice so that gc can see the base pointer in it.
  1576  	var x []unsafe.Pointer
  1577  
  1578  	// Reinterpret as *sliceHeader to edit.
  1579  	s := (*sliceHeader)(unsafe.Pointer(&x))
  1580  	s.Len = j - i
  1581  	s.Cap = cap - i
  1582  	if cap-i > 0 {
  1583  		s.Data = arrayAt(base, i, typ.elem.Size())
  1584  	} else {
  1585  		// do not advance pointer, to avoid pointing beyond end of slice
  1586  		s.Data = base
  1587  	}
  1588  
  1589  	fl := v.flag&flagRO | flagIndir | flag(Slice)
  1590  	return Value{typ.common(), unsafe.Pointer(&x), fl}
  1591  }
  1592  
  1593  // Slice3 is the 3-index form of the slice operation: it returns v[i:j:k].
  1594  // It panics if v's Kind is not Array or Slice, or if v is an unaddressable array,
  1595  // or if the indexes are out of bounds.
  1596  func (v Value) Slice3(i, j, k int) Value {
  1597  	var (
  1598  		cap  int
  1599  		typ  *sliceType
  1600  		base unsafe.Pointer
  1601  	)
  1602  	switch kind := v.kind(); kind {
  1603  	default:
  1604  		panic(&ValueError{"reflect.Value.Slice3", v.kind()})
  1605  
  1606  	case Array:
  1607  		if v.flag&flagAddr == 0 {
  1608  			panic("reflect.Value.Slice3: slice of unaddressable array")
  1609  		}
  1610  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1611  		cap = int(tt.len)
  1612  		typ = (*sliceType)(unsafe.Pointer(tt.slice))
  1613  		base = v.ptr
  1614  
  1615  	case Slice:
  1616  		typ = (*sliceType)(unsafe.Pointer(v.typ))
  1617  		s := (*sliceHeader)(v.ptr)
  1618  		base = s.Data
  1619  		cap = s.Cap
  1620  	}
  1621  
  1622  	if i < 0 || j < i || k < j || k > cap {
  1623  		panic("reflect.Value.Slice3: slice index out of bounds")
  1624  	}
  1625  
  1626  	// Declare slice so that the garbage collector
  1627  	// can see the base pointer in it.
  1628  	var x []unsafe.Pointer
  1629  
  1630  	// Reinterpret as *sliceHeader to edit.
  1631  	s := (*sliceHeader)(unsafe.Pointer(&x))
  1632  	s.Len = j - i
  1633  	s.Cap = k - i
  1634  	if k-i > 0 {
  1635  		s.Data = arrayAt(base, i, typ.elem.Size())
  1636  	} else {
  1637  		// do not advance pointer, to avoid pointing beyond end of slice
  1638  		s.Data = base
  1639  	}
  1640  
  1641  	fl := v.flag&flagRO | flagIndir | flag(Slice)
  1642  	return Value{typ.common(), unsafe.Pointer(&x), fl}
  1643  }
  1644  
  1645  // String returns the string v's underlying value, as a string.
  1646  // String is a special case because of Go's String method convention.
  1647  // Unlike the other getters, it does not panic if v's Kind is not String.
  1648  // Instead, it returns a string of the form "<T value>" where T is v's type.
  1649  // The fmt package treats Values specially. It does not call their String
  1650  // method implicitly but instead prints the concrete values they hold.
  1651  func (v Value) String() string {
  1652  	switch k := v.kind(); k {
  1653  	case Invalid:
  1654  		return "<invalid Value>"
  1655  	case String:
  1656  		return *(*string)(v.ptr)
  1657  	}
  1658  	// If you call String on a reflect.Value of other type, it's better to
  1659  	// print something than to panic. Useful in debugging.
  1660  	return "<" + v.Type().String() + " Value>"
  1661  }
  1662  
  1663  // TryRecv attempts to receive a value from the channel v but will not block.
  1664  // It panics if v's Kind is not Chan.
  1665  // If the receive delivers a value, x is the transferred value and ok is true.
  1666  // If the receive cannot finish without blocking, x is the zero Value and ok is false.
  1667  // If the channel is closed, x is the zero value for the channel's element type and ok is false.
  1668  func (v Value) TryRecv() (x Value, ok bool) {
  1669  	v.mustBe(Chan)
  1670  	v.mustBeExported()
  1671  	return v.recv(true)
  1672  }
  1673  
  1674  // TrySend attempts to send x on the channel v but will not block.
  1675  // It panics if v's Kind is not Chan.
  1676  // It reports whether the value was sent.
  1677  // As in Go, x's value must be assignable to the channel's element type.
  1678  func (v Value) TrySend(x Value) bool {
  1679  	v.mustBe(Chan)
  1680  	v.mustBeExported()
  1681  	return v.send(x, true)
  1682  }
  1683  
  1684  // Type returns v's type.
  1685  func (v Value) Type() Type {
  1686  	f := v.flag
  1687  	if f == 0 {
  1688  		panic(&ValueError{"reflect.Value.Type", Invalid})
  1689  	}
  1690  	if f&flagMethod == 0 {
  1691  		// Easy case
  1692  		return v.typ
  1693  	}
  1694  
  1695  	// Method value.
  1696  	// v.typ describes the receiver, not the method type.
  1697  	i := int(v.flag) >> flagMethodShift
  1698  	if v.typ.Kind() == Interface {
  1699  		// Method on interface.
  1700  		tt := (*interfaceType)(unsafe.Pointer(v.typ))
  1701  		if uint(i) >= uint(len(tt.methods)) {
  1702  			panic("reflect: internal error: invalid method index")
  1703  		}
  1704  		m := &tt.methods[i]
  1705  		return v.typ.typeOff(m.typ)
  1706  	}
  1707  	// Method on concrete type.
  1708  	ut := v.typ.uncommon()
  1709  	if ut == nil || uint(i) >= uint(ut.mcount) {
  1710  		panic("reflect: internal error: invalid method index")
  1711  	}
  1712  	m := ut.methods()[i]
  1713  	return v.typ.typeOff(m.mtyp)
  1714  }
  1715  
  1716  // Uint returns v's underlying value, as a uint64.
  1717  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
  1718  func (v Value) Uint() uint64 {
  1719  	k := v.kind()
  1720  	p := v.ptr
  1721  	switch k {
  1722  	case Uint:
  1723  		return uint64(*(*uint)(p))
  1724  	case Uint8:
  1725  		return uint64(*(*uint8)(p))
  1726  	case Uint16:
  1727  		return uint64(*(*uint16)(p))
  1728  	case Uint32:
  1729  		return uint64(*(*uint32)(p))
  1730  	case Uint64:
  1731  		return *(*uint64)(p)
  1732  	case Uintptr:
  1733  		return uint64(*(*uintptr)(p))
  1734  	}
  1735  	panic(&ValueError{"reflect.Value.Uint", v.kind()})
  1736  }
  1737  
  1738  // UnsafeAddr returns a pointer to v's data.
  1739  // It is for advanced clients that also import the "unsafe" package.
  1740  // It panics if v is not addressable.
  1741  func (v Value) UnsafeAddr() uintptr {
  1742  	// TODO: deprecate
  1743  	if v.typ == nil {
  1744  		panic(&ValueError{"reflect.Value.UnsafeAddr", Invalid})
  1745  	}
  1746  	if v.flag&flagAddr == 0 {
  1747  		panic("reflect.Value.UnsafeAddr of unaddressable value")
  1748  	}
  1749  	return uintptr(v.ptr)
  1750  }
  1751  
  1752  // StringHeader is the runtime representation of a string.
  1753  // It cannot be used safely or portably and its representation may
  1754  // change in a later release.
  1755  // Moreover, the Data field is not sufficient to guarantee the data
  1756  // it references will not be garbage collected, so programs must keep
  1757  // a separate, correctly typed pointer to the underlying data.
  1758  type StringHeader struct {
  1759  	Data uintptr
  1760  	Len  int
  1761  }
  1762  
  1763  // stringHeader is a safe version of StringHeader used within this package.
  1764  type stringHeader struct {
  1765  	Data unsafe.Pointer
  1766  	Len  int
  1767  }
  1768  
  1769  // SliceHeader is the runtime representation of a slice.
  1770  // It cannot be used safely or portably and its representation may
  1771  // change in a later release.
  1772  // Moreover, the Data field is not sufficient to guarantee the data
  1773  // it references will not be garbage collected, so programs must keep
  1774  // a separate, correctly typed pointer to the underlying data.
  1775  type SliceHeader struct {
  1776  	Data uintptr
  1777  	Len  int
  1778  	Cap  int
  1779  }
  1780  
  1781  // sliceHeader is a safe version of SliceHeader used within this package.
  1782  type sliceHeader struct {
  1783  	Data unsafe.Pointer
  1784  	Len  int
  1785  	Cap  int
  1786  }
  1787  
  1788  func typesMustMatch(what string, t1, t2 Type) {
  1789  	if t1 != t2 {
  1790  		panic(what + ": " + t1.String() + " != " + t2.String())
  1791  	}
  1792  }
  1793  
  1794  // arrayAt returns the i-th element of p, a C-array whose elements are
  1795  // eltSize wide (in bytes).
  1796  func arrayAt(p unsafe.Pointer, i int, eltSize uintptr) unsafe.Pointer {
  1797  	return unsafe.Pointer(uintptr(p) + uintptr(i)*eltSize)
  1798  }
  1799  
  1800  // grow grows the slice s so that it can hold extra more values, allocating
  1801  // more capacity if needed. It also returns the old and new slice lengths.
  1802  func grow(s Value, extra int) (Value, int, int) {
  1803  	i0 := s.Len()
  1804  	i1 := i0 + extra
  1805  	if i1 < i0 {
  1806  		panic("reflect.Append: slice overflow")
  1807  	}
  1808  	m := s.Cap()
  1809  	if i1 <= m {
  1810  		return s.Slice(0, i1), i0, i1
  1811  	}
  1812  	if m == 0 {
  1813  		m = extra
  1814  	} else {
  1815  		for m < i1 {
  1816  			if i0 < 1024 {
  1817  				m += m
  1818  			} else {
  1819  				m += m / 4
  1820  			}
  1821  		}
  1822  	}
  1823  	t := MakeSlice(s.Type(), i1, m)
  1824  	Copy(t, s)
  1825  	return t, i0, i1
  1826  }
  1827  
  1828  // Append appends the values x to a slice s and returns the resulting slice.
  1829  // As in Go, each x's value must be assignable to the slice's element type.
  1830  func Append(s Value, x ...Value) Value {
  1831  	s.mustBe(Slice)
  1832  	s, i0, i1 := grow(s, len(x))
  1833  	for i, j := i0, 0; i < i1; i, j = i+1, j+1 {
  1834  		s.Index(i).Set(x[j])
  1835  	}
  1836  	return s
  1837  }
  1838  
  1839  // AppendSlice appends a slice t to a slice s and returns the resulting slice.
  1840  // The slices s and t must have the same element type.
  1841  func AppendSlice(s, t Value) Value {
  1842  	s.mustBe(Slice)
  1843  	t.mustBe(Slice)
  1844  	typesMustMatch("reflect.AppendSlice", s.Type().Elem(), t.Type().Elem())
  1845  	s, i0, i1 := grow(s, t.Len())
  1846  	Copy(s.Slice(i0, i1), t)
  1847  	return s
  1848  }
  1849  
  1850  // Copy copies the contents of src into dst until either
  1851  // dst has been filled or src has been exhausted.
  1852  // It returns the number of elements copied.
  1853  // Dst and src each must have kind Slice or Array, and
  1854  // dst and src must have the same element type.
  1855  func Copy(dst, src Value) int {
  1856  	dk := dst.kind()
  1857  	if dk != Array && dk != Slice {
  1858  		panic(&ValueError{"reflect.Copy", dk})
  1859  	}
  1860  	if dk == Array {
  1861  		dst.mustBeAssignable()
  1862  	}
  1863  	dst.mustBeExported()
  1864  
  1865  	sk := src.kind()
  1866  	if sk != Array && sk != Slice {
  1867  		panic(&ValueError{"reflect.Copy", sk})
  1868  	}
  1869  	src.mustBeExported()
  1870  
  1871  	de := dst.typ.Elem()
  1872  	se := src.typ.Elem()
  1873  	typesMustMatch("reflect.Copy", de, se)
  1874  
  1875  	var ds, ss sliceHeader
  1876  	if dk == Array {
  1877  		ds.Data = dst.ptr
  1878  		ds.Len = dst.Len()
  1879  		ds.Cap = ds.Len
  1880  	} else {
  1881  		ds = *(*sliceHeader)(dst.ptr)
  1882  	}
  1883  	if sk == Array {
  1884  		ss.Data = src.ptr
  1885  		ss.Len = src.Len()
  1886  		ss.Cap = ss.Len
  1887  	} else {
  1888  		ss = *(*sliceHeader)(src.ptr)
  1889  	}
  1890  
  1891  	return typedslicecopy(de.common(), ds, ss)
  1892  }
  1893  
  1894  // A runtimeSelect is a single case passed to rselect.
  1895  // This must match ../runtime/select.go:/runtimeSelect
  1896  type runtimeSelect struct {
  1897  	dir SelectDir      // SelectSend, SelectRecv or SelectDefault
  1898  	typ *rtype         // channel type
  1899  	ch  unsafe.Pointer // channel
  1900  	val unsafe.Pointer // ptr to data (SendDir) or ptr to receive buffer (RecvDir)
  1901  }
  1902  
  1903  // rselect runs a select. It returns the index of the chosen case.
  1904  // If the case was a receive, val is filled in with the received value.
  1905  // The conventional OK bool indicates whether the receive corresponds
  1906  // to a sent value.
  1907  //go:noescape
  1908  func rselect([]runtimeSelect) (chosen int, recvOK bool)
  1909  
  1910  // A SelectDir describes the communication direction of a select case.
  1911  type SelectDir int
  1912  
  1913  // NOTE: These values must match ../runtime/select.go:/selectDir.
  1914  
  1915  const (
  1916  	_             SelectDir = iota
  1917  	SelectSend              // case Chan <- Send
  1918  	SelectRecv              // case <-Chan:
  1919  	SelectDefault           // default
  1920  )
  1921  
  1922  // A SelectCase describes a single case in a select operation.
  1923  // The kind of case depends on Dir, the communication direction.
  1924  //
  1925  // If Dir is SelectDefault, the case represents a default case.
  1926  // Chan and Send must be zero Values.
  1927  //
  1928  // If Dir is SelectSend, the case represents a send operation.
  1929  // Normally Chan's underlying value must be a channel, and Send's underlying value must be
  1930  // assignable to the channel's element type. As a special case, if Chan is a zero Value,
  1931  // then the case is ignored, and the field Send will also be ignored and may be either zero
  1932  // or non-zero.
  1933  //
  1934  // If Dir is SelectRecv, the case represents a receive operation.
  1935  // Normally Chan's underlying value must be a channel and Send must be a zero Value.
  1936  // If Chan is a zero Value, then the case is ignored, but Send must still be a zero Value.
  1937  // When a receive operation is selected, the received Value is returned by Select.
  1938  //
  1939  type SelectCase struct {
  1940  	Dir  SelectDir // direction of case
  1941  	Chan Value     // channel to use (for send or receive)
  1942  	Send Value     // value to send (for send)
  1943  }
  1944  
  1945  // Select executes a select operation described by the list of cases.
  1946  // Like the Go select statement, it blocks until at least one of the cases
  1947  // can proceed, makes a uniform pseudo-random choice,
  1948  // and then executes that case. It returns the index of the chosen case
  1949  // and, if that case was a receive operation, the value received and a
  1950  // boolean indicating whether the value corresponds to a send on the channel
  1951  // (as opposed to a zero value received because the channel is closed).
  1952  func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool) {
  1953  	// NOTE: Do not trust that caller is not modifying cases data underfoot.
  1954  	// The range is safe because the caller cannot modify our copy of the len
  1955  	// and each iteration makes its own copy of the value c.
  1956  	runcases := make([]runtimeSelect, len(cases))
  1957  	haveDefault := false
  1958  	for i, c := range cases {
  1959  		rc := &runcases[i]
  1960  		rc.dir = c.Dir
  1961  		switch c.Dir {
  1962  		default:
  1963  			panic("reflect.Select: invalid Dir")
  1964  
  1965  		case SelectDefault: // default
  1966  			if haveDefault {
  1967  				panic("reflect.Select: multiple default cases")
  1968  			}
  1969  			haveDefault = true
  1970  			if c.Chan.IsValid() {
  1971  				panic("reflect.Select: default case has Chan value")
  1972  			}
  1973  			if c.Send.IsValid() {
  1974  				panic("reflect.Select: default case has Send value")
  1975  			}
  1976  
  1977  		case SelectSend:
  1978  			ch := c.Chan
  1979  			if !ch.IsValid() {
  1980  				break
  1981  			}
  1982  			ch.mustBe(Chan)
  1983  			ch.mustBeExported()
  1984  			tt := (*chanType)(unsafe.Pointer(ch.typ))
  1985  			if ChanDir(tt.dir)&SendDir == 0 {
  1986  				panic("reflect.Select: SendDir case using recv-only channel")
  1987  			}
  1988  			rc.ch = ch.pointer()
  1989  			rc.typ = &tt.rtype
  1990  			v := c.Send
  1991  			if !v.IsValid() {
  1992  				panic("reflect.Select: SendDir case missing Send value")
  1993  			}
  1994  			v.mustBeExported()
  1995  			v = v.assignTo("reflect.Select", tt.elem, nil)
  1996  			if v.flag&flagIndir != 0 {
  1997  				rc.val = v.ptr
  1998  			} else {
  1999  				rc.val = unsafe.Pointer(&v.ptr)
  2000  			}
  2001  
  2002  		case SelectRecv:
  2003  			if c.Send.IsValid() {
  2004  				panic("reflect.Select: RecvDir case has Send value")
  2005  			}
  2006  			ch := c.Chan
  2007  			if !ch.IsValid() {
  2008  				break
  2009  			}
  2010  			ch.mustBe(Chan)
  2011  			ch.mustBeExported()
  2012  			tt := (*chanType)(unsafe.Pointer(ch.typ))
  2013  			if ChanDir(tt.dir)&RecvDir == 0 {
  2014  				panic("reflect.Select: RecvDir case using send-only channel")
  2015  			}
  2016  			rc.ch = ch.pointer()
  2017  			rc.typ = &tt.rtype
  2018  			rc.val = unsafe_New(tt.elem)
  2019  		}
  2020  	}
  2021  
  2022  	chosen, recvOK = rselect(runcases)
  2023  	if runcases[chosen].dir == SelectRecv {
  2024  		tt := (*chanType)(unsafe.Pointer(runcases[chosen].typ))
  2025  		t := tt.elem
  2026  		p := runcases[chosen].val
  2027  		fl := flag(t.Kind())
  2028  		if ifaceIndir(t) {
  2029  			recv = Value{t, p, fl | flagIndir}
  2030  		} else {
  2031  			recv = Value{t, *(*unsafe.Pointer)(p), fl}
  2032  		}
  2033  	}
  2034  	return chosen, recv, recvOK
  2035  }
  2036  
  2037  /*
  2038   * constructors
  2039   */
  2040  
  2041  // implemented in package runtime
  2042  func unsafe_New(*rtype) unsafe.Pointer
  2043  func unsafe_NewArray(*rtype, int) unsafe.Pointer
  2044  
  2045  // MakeSlice creates a new zero-initialized slice value
  2046  // for the specified slice type, length, and capacity.
  2047  func MakeSlice(typ Type, len, cap int) Value {
  2048  	if typ.Kind() != Slice {
  2049  		panic("reflect.MakeSlice of non-slice type")
  2050  	}
  2051  	if len < 0 {
  2052  		panic("reflect.MakeSlice: negative len")
  2053  	}
  2054  	if cap < 0 {
  2055  		panic("reflect.MakeSlice: negative cap")
  2056  	}
  2057  	if len > cap {
  2058  		panic("reflect.MakeSlice: len > cap")
  2059  	}
  2060  
  2061  	s := sliceHeader{unsafe_NewArray(typ.Elem().(*rtype), cap), len, cap}
  2062  	return Value{typ.common(), unsafe.Pointer(&s), flagIndir | flag(Slice)}
  2063  }
  2064  
  2065  // MakeChan creates a new channel with the specified type and buffer size.
  2066  func MakeChan(typ Type, buffer int) Value {
  2067  	if typ.Kind() != Chan {
  2068  		panic("reflect.MakeChan of non-chan type")
  2069  	}
  2070  	if buffer < 0 {
  2071  		panic("reflect.MakeChan: negative buffer size")
  2072  	}
  2073  	if typ.ChanDir() != BothDir {
  2074  		panic("reflect.MakeChan: unidirectional channel type")
  2075  	}
  2076  	ch := makechan(typ.(*rtype), uint64(buffer))
  2077  	return Value{typ.common(), ch, flag(Chan)}
  2078  }
  2079  
  2080  // MakeMap creates a new map with the specified type.
  2081  func MakeMap(typ Type) Value {
  2082  	return MakeMapWithSize(typ, 0)
  2083  }
  2084  
  2085  // MakeMapWithSize creates a new map with the specified type and initial capacity.
  2086  func MakeMapWithSize(typ Type, cap int) Value {
  2087  	if typ.Kind() != Map {
  2088  		panic("reflect.MakeMapWithSize of non-map type")
  2089  	}
  2090  	m := makemap(typ.(*rtype), cap)
  2091  	return Value{typ.common(), m, flag(Map)}
  2092  }
  2093  
  2094  // Indirect returns the value that v points to.
  2095  // If v is a nil pointer, Indirect returns a zero Value.
  2096  // If v is not a pointer, Indirect returns v.
  2097  func Indirect(v Value) Value {
  2098  	if v.Kind() != Ptr {
  2099  		return v
  2100  	}
  2101  	return v.Elem()
  2102  }
  2103  
  2104  // ValueOf returns a new Value initialized to the concrete value
  2105  // stored in the interface i. ValueOf(nil) returns the zero Value.
  2106  func ValueOf(i interface{}) Value {
  2107  	if i == nil {
  2108  		return Value{}
  2109  	}
  2110  
  2111  	// TODO: Maybe allow contents of a Value to live on the stack.
  2112  	// For now we make the contents always escape to the heap. It
  2113  	// makes life easier in a few places (see chanrecv/mapassign
  2114  	// comment below).
  2115  	escapes(i)
  2116  
  2117  	return unpackEface(i)
  2118  }
  2119  
  2120  // Zero returns a Value representing the zero value for the specified type.
  2121  // The result is different from the zero value of the Value struct,
  2122  // which represents no value at all.
  2123  // For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0.
  2124  // The returned value is neither addressable nor settable.
  2125  func Zero(typ Type) Value {
  2126  	if typ == nil {
  2127  		panic("reflect: Zero(nil)")
  2128  	}
  2129  	t := typ.common()
  2130  	fl := flag(t.Kind())
  2131  	if ifaceIndir(t) {
  2132  		return Value{t, unsafe_New(typ.(*rtype)), fl | flagIndir}
  2133  	}
  2134  	return Value{t, nil, fl}
  2135  }
  2136  
  2137  // New returns a Value representing a pointer to a new zero value
  2138  // for the specified type. That is, the returned Value's Type is PtrTo(typ).
  2139  func New(typ Type) Value {
  2140  	if typ == nil {
  2141  		panic("reflect: New(nil)")
  2142  	}
  2143  	ptr := unsafe_New(typ.(*rtype))
  2144  	fl := flag(Ptr)
  2145  	return Value{typ.common().ptrTo(), ptr, fl}
  2146  }
  2147  
  2148  // NewAt returns a Value representing a pointer to a value of the
  2149  // specified type, using p as that pointer.
  2150  func NewAt(typ Type, p unsafe.Pointer) Value {
  2151  	fl := flag(Ptr)
  2152  	return Value{typ.common().ptrTo(), p, fl}
  2153  }
  2154  
  2155  // assignTo returns a value v that can be assigned directly to typ.
  2156  // It panics if v is not assignable to typ.
  2157  // For a conversion to an interface type, target is a suggested scratch space to use.
  2158  func (v Value) assignTo(context string, dst *rtype, target unsafe.Pointer) Value {
  2159  	if v.flag&flagMethod != 0 {
  2160  		v = makeMethodValue(context, v)
  2161  	}
  2162  
  2163  	switch {
  2164  	case directlyAssignable(dst, v.typ):
  2165  		// Overwrite type so that they match.
  2166  		// Same memory layout, so no harm done.
  2167  		fl := v.flag & (flagRO | flagAddr | flagIndir)
  2168  		fl |= flag(dst.Kind())
  2169  		return Value{dst, v.ptr, fl}
  2170  
  2171  	case implements(dst, v.typ):
  2172  		if target == nil {
  2173  			target = unsafe_New(dst)
  2174  		}
  2175  		x := valueInterface(v, false)
  2176  		if dst.NumMethod() == 0 {
  2177  			*(*interface{})(target) = x
  2178  		} else {
  2179  			ifaceE2I(dst, x, target)
  2180  		}
  2181  		return Value{dst, target, flagIndir | flag(Interface)}
  2182  	}
  2183  
  2184  	// Failed.
  2185  	panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String())
  2186  }
  2187  
  2188  // Convert returns the value v converted to type t.
  2189  // If the usual Go conversion rules do not allow conversion
  2190  // of the value v to type t, Convert panics.
  2191  func (v Value) Convert(t Type) Value {
  2192  	if v.flag&flagMethod != 0 {
  2193  		v = makeMethodValue("Convert", v)
  2194  	}
  2195  	op := convertOp(t.common(), v.typ)
  2196  	if op == nil {
  2197  		panic("reflect.Value.Convert: value of type " + v.typ.String() + " cannot be converted to type " + t.String())
  2198  	}
  2199  	return op(v, t)
  2200  }
  2201  
  2202  // convertOp returns the function to convert a value of type src
  2203  // to a value of type dst. If the conversion is illegal, convertOp returns nil.
  2204  func convertOp(dst, src *rtype) func(Value, Type) Value {
  2205  	switch src.Kind() {
  2206  	case Int, Int8, Int16, Int32, Int64:
  2207  		switch dst.Kind() {
  2208  		case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2209  			return cvtInt
  2210  		case Float32, Float64:
  2211  			return cvtIntFloat
  2212  		case String:
  2213  			return cvtIntString
  2214  		}
  2215  
  2216  	case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2217  		switch dst.Kind() {
  2218  		case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2219  			return cvtUint
  2220  		case Float32, Float64:
  2221  			return cvtUintFloat
  2222  		case String:
  2223  			return cvtUintString
  2224  		}
  2225  
  2226  	case Float32, Float64:
  2227  		switch dst.Kind() {
  2228  		case Int, Int8, Int16, Int32, Int64:
  2229  			return cvtFloatInt
  2230  		case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2231  			return cvtFloatUint
  2232  		case Float32, Float64:
  2233  			return cvtFloat
  2234  		}
  2235  
  2236  	case Complex64, Complex128:
  2237  		switch dst.Kind() {
  2238  		case Complex64, Complex128:
  2239  			return cvtComplex
  2240  		}
  2241  
  2242  	case String:
  2243  		if dst.Kind() == Slice && dst.Elem().PkgPath() == "" {
  2244  			switch dst.Elem().Kind() {
  2245  			case Uint8:
  2246  				return cvtStringBytes
  2247  			case Int32:
  2248  				return cvtStringRunes
  2249  			}
  2250  		}
  2251  
  2252  	case Slice:
  2253  		if dst.Kind() == String && src.Elem().PkgPath() == "" {
  2254  			switch src.Elem().Kind() {
  2255  			case Uint8:
  2256  				return cvtBytesString
  2257  			case Int32:
  2258  				return cvtRunesString
  2259  			}
  2260  		}
  2261  	}
  2262  
  2263  	// dst and src have same underlying type.
  2264  	if haveIdenticalUnderlyingType(dst, src, false) {
  2265  		return cvtDirect
  2266  	}
  2267  
  2268  	// dst and src are unnamed pointer types with same underlying base type.
  2269  	if dst.Kind() == Ptr && dst.Name() == "" &&
  2270  		src.Kind() == Ptr && src.Name() == "" &&
  2271  		haveIdenticalUnderlyingType(dst.Elem().common(), src.Elem().common(), false) {
  2272  		return cvtDirect
  2273  	}
  2274  
  2275  	if implements(dst, src) {
  2276  		if src.Kind() == Interface {
  2277  			return cvtI2I
  2278  		}
  2279  		return cvtT2I
  2280  	}
  2281  
  2282  	return nil
  2283  }
  2284  
  2285  // makeInt returns a Value of type t equal to bits (possibly truncated),
  2286  // where t is a signed or unsigned int type.
  2287  func makeInt(f flag, bits uint64, t Type) Value {
  2288  	typ := t.common()
  2289  	ptr := unsafe_New(typ)
  2290  	switch typ.size {
  2291  	case 1:
  2292  		*(*uint8)(ptr) = uint8(bits)
  2293  	case 2:
  2294  		*(*uint16)(ptr) = uint16(bits)
  2295  	case 4:
  2296  		*(*uint32)(ptr) = uint32(bits)
  2297  	case 8:
  2298  		*(*uint64)(ptr) = bits
  2299  	}
  2300  	return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
  2301  }
  2302  
  2303  // makeFloat returns a Value of type t equal to v (possibly truncated to float32),
  2304  // where t is a float32 or float64 type.
  2305  func makeFloat(f flag, v float64, t Type) Value {
  2306  	typ := t.common()
  2307  	ptr := unsafe_New(typ)
  2308  	switch typ.size {
  2309  	case 4:
  2310  		*(*float32)(ptr) = float32(v)
  2311  	case 8:
  2312  		*(*float64)(ptr) = v
  2313  	}
  2314  	return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
  2315  }
  2316  
  2317  // makeComplex returns a Value of type t equal to v (possibly truncated to complex64),
  2318  // where t is a complex64 or complex128 type.
  2319  func makeComplex(f flag, v complex128, t Type) Value {
  2320  	typ := t.common()
  2321  	ptr := unsafe_New(typ)
  2322  	switch typ.size {
  2323  	case 8:
  2324  		*(*complex64)(ptr) = complex64(v)
  2325  	case 16:
  2326  		*(*complex128)(ptr) = v
  2327  	}
  2328  	return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
  2329  }
  2330  
  2331  func makeString(f flag, v string, t Type) Value {
  2332  	ret := New(t).Elem()
  2333  	ret.SetString(v)
  2334  	ret.flag = ret.flag&^flagAddr | f
  2335  	return ret
  2336  }
  2337  
  2338  func makeBytes(f flag, v []byte, t Type) Value {
  2339  	ret := New(t).Elem()
  2340  	ret.SetBytes(v)
  2341  	ret.flag = ret.flag&^flagAddr | f
  2342  	return ret
  2343  }
  2344  
  2345  func makeRunes(f flag, v []rune, t Type) Value {
  2346  	ret := New(t).Elem()
  2347  	ret.setRunes(v)
  2348  	ret.flag = ret.flag&^flagAddr | f
  2349  	return ret
  2350  }
  2351  
  2352  // These conversion functions are returned by convertOp
  2353  // for classes of conversions. For example, the first function, cvtInt,
  2354  // takes any value v of signed int type and returns the value converted
  2355  // to type t, where t is any signed or unsigned int type.
  2356  
  2357  // convertOp: intXX -> [u]intXX
  2358  func cvtInt(v Value, t Type) Value {
  2359  	return makeInt(v.flag&flagRO, uint64(v.Int()), t)
  2360  }
  2361  
  2362  // convertOp: uintXX -> [u]intXX
  2363  func cvtUint(v Value, t Type) Value {
  2364  	return makeInt(v.flag&flagRO, v.Uint(), t)
  2365  }
  2366  
  2367  // convertOp: floatXX -> intXX
  2368  func cvtFloatInt(v Value, t Type) Value {
  2369  	return makeInt(v.flag&flagRO, uint64(int64(v.Float())), t)
  2370  }
  2371  
  2372  // convertOp: floatXX -> uintXX
  2373  func cvtFloatUint(v Value, t Type) Value {
  2374  	return makeInt(v.flag&flagRO, uint64(v.Float()), t)
  2375  }
  2376  
  2377  // convertOp: intXX -> floatXX
  2378  func cvtIntFloat(v Value, t Type) Value {
  2379  	return makeFloat(v.flag&flagRO, float64(v.Int()), t)
  2380  }
  2381  
  2382  // convertOp: uintXX -> floatXX
  2383  func cvtUintFloat(v Value, t Type) Value {
  2384  	return makeFloat(v.flag&flagRO, float64(v.Uint()), t)
  2385  }
  2386  
  2387  // convertOp: floatXX -> floatXX
  2388  func cvtFloat(v Value, t Type) Value {
  2389  	return makeFloat(v.flag&flagRO, v.Float(), t)
  2390  }
  2391  
  2392  // convertOp: complexXX -> complexXX
  2393  func cvtComplex(v Value, t Type) Value {
  2394  	return makeComplex(v.flag&flagRO, v.Complex(), t)
  2395  }
  2396  
  2397  // convertOp: intXX -> string
  2398  func cvtIntString(v Value, t Type) Value {
  2399  	return makeString(v.flag&flagRO, string(v.Int()), t)
  2400  }
  2401  
  2402  // convertOp: uintXX -> string
  2403  func cvtUintString(v Value, t Type) Value {
  2404  	return makeString(v.flag&flagRO, string(v.Uint()), t)
  2405  }
  2406  
  2407  // convertOp: []byte -> string
  2408  func cvtBytesString(v Value, t Type) Value {
  2409  	return makeString(v.flag&flagRO, string(v.Bytes()), t)
  2410  }
  2411  
  2412  // convertOp: string -> []byte
  2413  func cvtStringBytes(v Value, t Type) Value {
  2414  	return makeBytes(v.flag&flagRO, []byte(v.String()), t)
  2415  }
  2416  
  2417  // convertOp: []rune -> string
  2418  func cvtRunesString(v Value, t Type) Value {
  2419  	return makeString(v.flag&flagRO, string(v.runes()), t)
  2420  }
  2421  
  2422  // convertOp: string -> []rune
  2423  func cvtStringRunes(v Value, t Type) Value {
  2424  	return makeRunes(v.flag&flagRO, []rune(v.String()), t)
  2425  }
  2426  
  2427  // convertOp: direct copy
  2428  func cvtDirect(v Value, typ Type) Value {
  2429  	f := v.flag
  2430  	t := typ.common()
  2431  	ptr := v.ptr
  2432  	if f&flagAddr != 0 {
  2433  		// indirect, mutable word - make a copy
  2434  		c := unsafe_New(t)
  2435  		typedmemmove(t, c, ptr)
  2436  		ptr = c
  2437  		f &^= flagAddr
  2438  	}
  2439  	return Value{t, ptr, v.flag&flagRO | f} // v.flag&flagRO|f == f?
  2440  }
  2441  
  2442  // convertOp: concrete -> interface
  2443  func cvtT2I(v Value, typ Type) Value {
  2444  	target := unsafe_New(typ.common())
  2445  	x := valueInterface(v, false)
  2446  	if typ.NumMethod() == 0 {
  2447  		*(*interface{})(target) = x
  2448  	} else {
  2449  		ifaceE2I(typ.(*rtype), x, target)
  2450  	}
  2451  	return Value{typ.common(), target, v.flag&flagRO | flagIndir | flag(Interface)}
  2452  }
  2453  
  2454  // convertOp: interface -> interface
  2455  func cvtI2I(v Value, typ Type) Value {
  2456  	if v.IsNil() {
  2457  		ret := Zero(typ)
  2458  		ret.flag |= v.flag & flagRO
  2459  		return ret
  2460  	}
  2461  	return cvtT2I(v.Elem(), typ)
  2462  }
  2463  
  2464  // implemented in ../runtime
  2465  func chancap(ch unsafe.Pointer) int
  2466  func chanclose(ch unsafe.Pointer)
  2467  func chanlen(ch unsafe.Pointer) int
  2468  
  2469  // Note: some of the noescape annotations below are technically a lie,
  2470  // but safe in the context of this package. Functions like chansend
  2471  // and mapassign don't escape the referent, but may escape anything
  2472  // the referent points to (they do shallow copies of the referent).
  2473  // It is safe in this package because the referent may only point
  2474  // to something a Value may point to, and that is always in the heap
  2475  // (due to the escapes() call in ValueOf).
  2476  
  2477  //go:noescape
  2478  func chanrecv(ch unsafe.Pointer, nb bool, val unsafe.Pointer) (selected, received bool)
  2479  
  2480  //go:noescape
  2481  func chansend(ch unsafe.Pointer, val unsafe.Pointer, nb bool) bool
  2482  
  2483  func makechan(typ *rtype, size uint64) (ch unsafe.Pointer)
  2484  func makemap(t *rtype, cap int) (m unsafe.Pointer)
  2485  
  2486  //go:noescape
  2487  func mapaccess(t *rtype, m unsafe.Pointer, key unsafe.Pointer) (val unsafe.Pointer)
  2488  
  2489  //go:noescape
  2490  func mapassign(t *rtype, m unsafe.Pointer, key, val unsafe.Pointer)
  2491  
  2492  //go:noescape
  2493  func mapdelete(t *rtype, m unsafe.Pointer, key unsafe.Pointer)
  2494  
  2495  // m escapes into the return value, but the caller of mapiterinit
  2496  // doesn't let the return value escape.
  2497  //go:noescape
  2498  func mapiterinit(t *rtype, m unsafe.Pointer) unsafe.Pointer
  2499  
  2500  //go:noescape
  2501  func mapiterkey(it unsafe.Pointer) (key unsafe.Pointer)
  2502  
  2503  //go:noescape
  2504  func mapiternext(it unsafe.Pointer)
  2505  
  2506  //go:noescape
  2507  func maplen(m unsafe.Pointer) int
  2508  
  2509  // call calls fn with a copy of the n argument bytes pointed at by arg.
  2510  // After fn returns, reflectcall copies n-retoffset result bytes
  2511  // back into arg+retoffset before returning. If copying result bytes back,
  2512  // the caller must pass the argument frame type as argtype, so that
  2513  // call can execute appropriate write barriers during the copy.
  2514  func call(argtype *rtype, fn, arg unsafe.Pointer, n uint32, retoffset uint32)
  2515  
  2516  func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)
  2517  
  2518  // typedmemmove copies a value of type t to dst from src.
  2519  //go:noescape
  2520  func typedmemmove(t *rtype, dst, src unsafe.Pointer)
  2521  
  2522  // typedmemmovepartial is like typedmemmove but assumes that
  2523  // dst and src point off bytes into the value and only copies size bytes.
  2524  //go:noescape
  2525  func typedmemmovepartial(t *rtype, dst, src unsafe.Pointer, off, size uintptr)
  2526  
  2527  // typedslicecopy copies a slice of elemType values from src to dst,
  2528  // returning the number of elements copied.
  2529  //go:noescape
  2530  func typedslicecopy(elemType *rtype, dst, src sliceHeader) int
  2531  
  2532  //go:noescape
  2533  func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)
  2534  
  2535  // Dummy annotation marking that the value x escapes,
  2536  // for use in cases where the reflect code is so clever that
  2537  // the compiler cannot follow.
  2538  func escapes(x interface{}) {
  2539  	if dummy.b {
  2540  		dummy.x = x
  2541  	}
  2542  }
  2543  
  2544  var dummy struct {
  2545  	b bool
  2546  	x interface{}
  2547  }