github.com/rohankumardubey/syslog-redirector-golang@v0.0.0-20140320174030-4859f03d829a/src/pkg/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  	"strconv"
    11  	"unsafe"
    12  )
    13  
    14  const bigEndian = false // can be smarter if we find a big-endian machine
    15  const ptrSize = unsafe.Sizeof((*byte)(nil))
    16  const cannotSet = "cannot set value obtained from unexported struct field"
    17  
    18  // TODO: This will have to go away when
    19  // the new gc goes in.
    20  func memmove(adst, asrc unsafe.Pointer, n uintptr) {
    21  	dst := uintptr(adst)
    22  	src := uintptr(asrc)
    23  	switch {
    24  	case src < dst && src+n > dst:
    25  		// byte copy backward
    26  		// careful: i is unsigned
    27  		for i := n; i > 0; {
    28  			i--
    29  			*(*byte)(unsafe.Pointer(dst + i)) = *(*byte)(unsafe.Pointer(src + i))
    30  		}
    31  	case (n|src|dst)&(ptrSize-1) != 0:
    32  		// byte copy forward
    33  		for i := uintptr(0); i < n; i++ {
    34  			*(*byte)(unsafe.Pointer(dst + i)) = *(*byte)(unsafe.Pointer(src + i))
    35  		}
    36  	default:
    37  		// word copy forward
    38  		for i := uintptr(0); i < n; i += ptrSize {
    39  			*(*uintptr)(unsafe.Pointer(dst + i)) = *(*uintptr)(unsafe.Pointer(src + i))
    40  		}
    41  	}
    42  }
    43  
    44  // Value is the reflection interface to a Go value.
    45  //
    46  // Not all methods apply to all kinds of values.  Restrictions,
    47  // if any, are noted in the documentation for each method.
    48  // Use the Kind method to find out the kind of value before
    49  // calling kind-specific methods.  Calling a method
    50  // inappropriate to the kind of type causes a run time panic.
    51  //
    52  // The zero Value represents no value.
    53  // Its IsValid method returns false, its Kind method returns Invalid,
    54  // its String method returns "<invalid Value>", and all other methods panic.
    55  // Most functions and methods never return an invalid value.
    56  // If one does, its documentation states the conditions explicitly.
    57  //
    58  // A Value can be used concurrently by multiple goroutines provided that
    59  // the underlying Go value can be used concurrently for the equivalent
    60  // direct operations.
    61  type Value struct {
    62  	// typ holds the type of the value represented by a Value.
    63  	typ *rtype
    64  
    65  	// val holds the 1-word representation of the value.
    66  	// If flag's flagIndir bit is set, then val is a pointer to the data.
    67  	// Otherwise val is a word holding the actual data.
    68  	// When the data is smaller than a word, it begins at
    69  	// the first byte (in the memory address sense) of val.
    70  	// We use unsafe.Pointer so that the garbage collector
    71  	// knows that val could be a pointer.
    72  	val unsafe.Pointer
    73  
    74  	// flag holds metadata about the value.
    75  	// The lowest bits are flag bits:
    76  	//	- flagRO: obtained via unexported field, so read-only
    77  	//	- flagIndir: val holds a pointer to the data
    78  	//	- flagAddr: v.CanAddr is true (implies flagIndir)
    79  	//	- flagMethod: v is a method value.
    80  	// The next five bits give the Kind of the value.
    81  	// This repeats typ.Kind() except for method values.
    82  	// The remaining 23+ bits give a method number for method values.
    83  	// If flag.kind() != Func, code can assume that flagMethod is unset.
    84  	// If typ.size > ptrSize, code can assume that flagIndir is set.
    85  	flag
    86  
    87  	// A method value represents a curried method invocation
    88  	// like r.Read for some receiver r.  The typ+val+flag bits describe
    89  	// the receiver r, but the flag's Kind bits say Func (methods are
    90  	// functions), and the top bits of the flag give the method number
    91  	// in r's type's method table.
    92  }
    93  
    94  type flag uintptr
    95  
    96  const (
    97  	flagRO flag = 1 << iota
    98  	flagIndir
    99  	flagAddr
   100  	flagMethod
   101  	flagKindShift        = iota
   102  	flagKindWidth        = 5 // there are 27 kinds
   103  	flagKindMask    flag = 1<<flagKindWidth - 1
   104  	flagMethodShift      = flagKindShift + flagKindWidth
   105  )
   106  
   107  func (f flag) kind() Kind {
   108  	return Kind((f >> flagKindShift) & flagKindMask)
   109  }
   110  
   111  // A ValueError occurs when a Value method is invoked on
   112  // a Value that does not support it.  Such cases are documented
   113  // in the description of each method.
   114  type ValueError struct {
   115  	Method string
   116  	Kind   Kind
   117  }
   118  
   119  func (e *ValueError) Error() string {
   120  	if e.Kind == 0 {
   121  		return "reflect: call of " + e.Method + " on zero Value"
   122  	}
   123  	return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value"
   124  }
   125  
   126  // methodName returns the name of the calling method,
   127  // assumed to be two stack frames above.
   128  func methodName() string {
   129  	pc, _, _, _ := runtime.Caller(2)
   130  	f := runtime.FuncForPC(pc)
   131  	if f == nil {
   132  		return "unknown method"
   133  	}
   134  	return f.Name()
   135  }
   136  
   137  // An iword is the word that would be stored in an
   138  // interface to represent a given value v.  Specifically, if v is
   139  // bigger than a pointer, its word is a pointer to v's data.
   140  // Otherwise, its word holds the data stored
   141  // in its leading bytes (so is not a pointer).
   142  // Because the value sometimes holds a pointer, we use
   143  // unsafe.Pointer to represent it, so that if iword appears
   144  // in a struct, the garbage collector knows that might be
   145  // a pointer.
   146  type iword unsafe.Pointer
   147  
   148  func (v Value) iword() iword {
   149  	if v.flag&flagIndir != 0 && v.typ.size <= ptrSize {
   150  		// Have indirect but want direct word.
   151  		return loadIword(v.val, v.typ.size)
   152  	}
   153  	return iword(v.val)
   154  }
   155  
   156  // loadIword loads n bytes at p from memory into an iword.
   157  func loadIword(p unsafe.Pointer, n uintptr) iword {
   158  	// Run the copy ourselves instead of calling memmove
   159  	// to avoid moving w to the heap.
   160  	var w iword
   161  	switch n {
   162  	default:
   163  		panic("reflect: internal error: loadIword of " + strconv.Itoa(int(n)) + "-byte value")
   164  	case 0:
   165  	case 1:
   166  		*(*uint8)(unsafe.Pointer(&w)) = *(*uint8)(p)
   167  	case 2:
   168  		*(*uint16)(unsafe.Pointer(&w)) = *(*uint16)(p)
   169  	case 3:
   170  		*(*[3]byte)(unsafe.Pointer(&w)) = *(*[3]byte)(p)
   171  	case 4:
   172  		*(*uint32)(unsafe.Pointer(&w)) = *(*uint32)(p)
   173  	case 5:
   174  		*(*[5]byte)(unsafe.Pointer(&w)) = *(*[5]byte)(p)
   175  	case 6:
   176  		*(*[6]byte)(unsafe.Pointer(&w)) = *(*[6]byte)(p)
   177  	case 7:
   178  		*(*[7]byte)(unsafe.Pointer(&w)) = *(*[7]byte)(p)
   179  	case 8:
   180  		*(*uint64)(unsafe.Pointer(&w)) = *(*uint64)(p)
   181  	}
   182  	return w
   183  }
   184  
   185  // storeIword stores n bytes from w into p.
   186  func storeIword(p unsafe.Pointer, w iword, n uintptr) {
   187  	// Run the copy ourselves instead of calling memmove
   188  	// to avoid moving w to the heap.
   189  	switch n {
   190  	default:
   191  		panic("reflect: internal error: storeIword of " + strconv.Itoa(int(n)) + "-byte value")
   192  	case 0:
   193  	case 1:
   194  		*(*uint8)(p) = *(*uint8)(unsafe.Pointer(&w))
   195  	case 2:
   196  		*(*uint16)(p) = *(*uint16)(unsafe.Pointer(&w))
   197  	case 3:
   198  		*(*[3]byte)(p) = *(*[3]byte)(unsafe.Pointer(&w))
   199  	case 4:
   200  		*(*uint32)(p) = *(*uint32)(unsafe.Pointer(&w))
   201  	case 5:
   202  		*(*[5]byte)(p) = *(*[5]byte)(unsafe.Pointer(&w))
   203  	case 6:
   204  		*(*[6]byte)(p) = *(*[6]byte)(unsafe.Pointer(&w))
   205  	case 7:
   206  		*(*[7]byte)(p) = *(*[7]byte)(unsafe.Pointer(&w))
   207  	case 8:
   208  		*(*uint64)(p) = *(*uint64)(unsafe.Pointer(&w))
   209  	}
   210  }
   211  
   212  // emptyInterface is the header for an interface{} value.
   213  type emptyInterface struct {
   214  	typ  *rtype
   215  	word iword
   216  }
   217  
   218  // nonEmptyInterface is the header for a interface value with methods.
   219  type nonEmptyInterface struct {
   220  	// see ../runtime/iface.c:/Itab
   221  	itab *struct {
   222  		ityp   *rtype // static interface type
   223  		typ    *rtype // dynamic concrete type
   224  		link   unsafe.Pointer
   225  		bad    int32
   226  		unused int32
   227  		fun    [100000]unsafe.Pointer // method table
   228  	}
   229  	word iword
   230  }
   231  
   232  // mustBe panics if f's kind is not expected.
   233  // Making this a method on flag instead of on Value
   234  // (and embedding flag in Value) means that we can write
   235  // the very clear v.mustBe(Bool) and have it compile into
   236  // v.flag.mustBe(Bool), which will only bother to copy the
   237  // single important word for the receiver.
   238  func (f flag) mustBe(expected Kind) {
   239  	k := f.kind()
   240  	if k != expected {
   241  		panic(&ValueError{methodName(), k})
   242  	}
   243  }
   244  
   245  // mustBeExported panics if f records that the value was obtained using
   246  // an unexported field.
   247  func (f flag) mustBeExported() {
   248  	if f == 0 {
   249  		panic(&ValueError{methodName(), 0})
   250  	}
   251  	if f&flagRO != 0 {
   252  		panic("reflect: " + methodName() + " using value obtained using unexported field")
   253  	}
   254  }
   255  
   256  // mustBeAssignable panics if f records that the value is not assignable,
   257  // which is to say that either it was obtained using an unexported field
   258  // or it is not addressable.
   259  func (f flag) mustBeAssignable() {
   260  	if f == 0 {
   261  		panic(&ValueError{methodName(), Invalid})
   262  	}
   263  	// Assignable if addressable and not read-only.
   264  	if f&flagRO != 0 {
   265  		panic("reflect: " + methodName() + " using value obtained using unexported field")
   266  	}
   267  	if f&flagAddr == 0 {
   268  		panic("reflect: " + methodName() + " using unaddressable value")
   269  	}
   270  }
   271  
   272  // Addr returns a pointer value representing the address of v.
   273  // It panics if CanAddr() returns false.
   274  // Addr is typically used to obtain a pointer to a struct field
   275  // or slice element in order to call a method that requires a
   276  // pointer receiver.
   277  func (v Value) Addr() Value {
   278  	if v.flag&flagAddr == 0 {
   279  		panic("reflect.Value.Addr of unaddressable value")
   280  	}
   281  	return Value{v.typ.ptrTo(), v.val, (v.flag & flagRO) | flag(Ptr)<<flagKindShift}
   282  }
   283  
   284  // Bool returns v's underlying value.
   285  // It panics if v's kind is not Bool.
   286  func (v Value) Bool() bool {
   287  	v.mustBe(Bool)
   288  	if v.flag&flagIndir != 0 {
   289  		return *(*bool)(v.val)
   290  	}
   291  	return *(*bool)(unsafe.Pointer(&v.val))
   292  }
   293  
   294  // Bytes returns v's underlying value.
   295  // It panics if v's underlying value is not a slice of bytes.
   296  func (v Value) Bytes() []byte {
   297  	v.mustBe(Slice)
   298  	if v.typ.Elem().Kind() != Uint8 {
   299  		panic("reflect.Value.Bytes of non-byte slice")
   300  	}
   301  	// Slice is always bigger than a word; assume flagIndir.
   302  	return *(*[]byte)(v.val)
   303  }
   304  
   305  // runes returns v's underlying value.
   306  // It panics if v's underlying value is not a slice of runes (int32s).
   307  func (v Value) runes() []rune {
   308  	v.mustBe(Slice)
   309  	if v.typ.Elem().Kind() != Int32 {
   310  		panic("reflect.Value.Bytes of non-rune slice")
   311  	}
   312  	// Slice is always bigger than a word; assume flagIndir.
   313  	return *(*[]rune)(v.val)
   314  }
   315  
   316  // CanAddr returns true if the value's address can be obtained with Addr.
   317  // Such values are called addressable.  A value is addressable if it is
   318  // an element of a slice, an element of an addressable array,
   319  // a field of an addressable struct, or the result of dereferencing a pointer.
   320  // If CanAddr returns false, calling Addr will panic.
   321  func (v Value) CanAddr() bool {
   322  	return v.flag&flagAddr != 0
   323  }
   324  
   325  // CanSet returns true if the value of v can be changed.
   326  // A Value can be changed only if it is addressable and was not
   327  // obtained by the use of unexported struct fields.
   328  // If CanSet returns false, calling Set or any type-specific
   329  // setter (e.g., SetBool, SetInt64) will panic.
   330  func (v Value) CanSet() bool {
   331  	return v.flag&(flagAddr|flagRO) == flagAddr
   332  }
   333  
   334  // Call calls the function v with the input arguments in.
   335  // For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]).
   336  // Call panics if v's Kind is not Func.
   337  // It returns the output results as Values.
   338  // As in Go, each input argument must be assignable to the
   339  // type of the function's corresponding input parameter.
   340  // If v is a variadic function, Call creates the variadic slice parameter
   341  // itself, copying in the corresponding values.
   342  func (v Value) Call(in []Value) []Value {
   343  	v.mustBe(Func)
   344  	v.mustBeExported()
   345  	return v.call("Call", in)
   346  }
   347  
   348  // CallSlice calls the variadic function v with the input arguments in,
   349  // assigning the slice in[len(in)-1] to v's final variadic argument.
   350  // For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]...).
   351  // Call panics if v's Kind is not Func or if v is not variadic.
   352  // It returns the output results as Values.
   353  // As in Go, each input argument must be assignable to the
   354  // type of the function's corresponding input parameter.
   355  func (v Value) CallSlice(in []Value) []Value {
   356  	v.mustBe(Func)
   357  	v.mustBeExported()
   358  	return v.call("CallSlice", in)
   359  }
   360  
   361  func (v Value) call(op string, in []Value) []Value {
   362  	// Get function pointer, type.
   363  	t := v.typ
   364  	var (
   365  		fn   unsafe.Pointer
   366  		rcvr iword
   367  	)
   368  	if v.flag&flagMethod != 0 {
   369  		t, fn, rcvr = methodReceiver(op, v, int(v.flag)>>flagMethodShift)
   370  	} else if v.flag&flagIndir != 0 {
   371  		fn = *(*unsafe.Pointer)(v.val)
   372  	} else {
   373  		fn = v.val
   374  	}
   375  
   376  	if fn == nil {
   377  		panic("reflect.Value.Call: call of nil function")
   378  	}
   379  
   380  	isSlice := op == "CallSlice"
   381  	n := t.NumIn()
   382  	if isSlice {
   383  		if !t.IsVariadic() {
   384  			panic("reflect: CallSlice of non-variadic function")
   385  		}
   386  		if len(in) < n {
   387  			panic("reflect: CallSlice with too few input arguments")
   388  		}
   389  		if len(in) > n {
   390  			panic("reflect: CallSlice with too many input arguments")
   391  		}
   392  	} else {
   393  		if t.IsVariadic() {
   394  			n--
   395  		}
   396  		if len(in) < n {
   397  			panic("reflect: Call with too few input arguments")
   398  		}
   399  		if !t.IsVariadic() && len(in) > n {
   400  			panic("reflect: Call with too many input arguments")
   401  		}
   402  	}
   403  	for _, x := range in {
   404  		if x.Kind() == Invalid {
   405  			panic("reflect: " + op + " using zero Value argument")
   406  		}
   407  	}
   408  	for i := 0; i < n; i++ {
   409  		if xt, targ := in[i].Type(), t.In(i); !xt.AssignableTo(targ) {
   410  			panic("reflect: " + op + " using " + xt.String() + " as type " + targ.String())
   411  		}
   412  	}
   413  	if !isSlice && t.IsVariadic() {
   414  		// prepare slice for remaining values
   415  		m := len(in) - n
   416  		slice := MakeSlice(t.In(n), m, m)
   417  		elem := t.In(n).Elem()
   418  		for i := 0; i < m; i++ {
   419  			x := in[n+i]
   420  			if xt := x.Type(); !xt.AssignableTo(elem) {
   421  				panic("reflect: cannot use " + xt.String() + " as type " + elem.String() + " in " + op)
   422  			}
   423  			slice.Index(i).Set(x)
   424  		}
   425  		origIn := in
   426  		in = make([]Value, n+1)
   427  		copy(in[:n], origIn)
   428  		in[n] = slice
   429  	}
   430  
   431  	nin := len(in)
   432  	if nin != t.NumIn() {
   433  		panic("reflect.Value.Call: wrong argument count")
   434  	}
   435  	nout := t.NumOut()
   436  
   437  	// Compute arg size & allocate.
   438  	// This computation is 5g/6g/8g-dependent
   439  	// and probably wrong for gccgo, but so
   440  	// is most of this function.
   441  	size, _, _, _ := frameSize(t, v.flag&flagMethod != 0)
   442  
   443  	// Copy into args.
   444  	//
   445  	// TODO(rsc): This will need to be updated for any new garbage collector.
   446  	// For now make everything look like a pointer by allocating
   447  	// a []unsafe.Pointer.
   448  	args := make([]unsafe.Pointer, size/ptrSize)
   449  	ptr := unsafe.Pointer(&args[0])
   450  	off := uintptr(0)
   451  	if v.flag&flagMethod != 0 {
   452  		// Hard-wired first argument.
   453  		*(*iword)(ptr) = rcvr
   454  		off = ptrSize
   455  	}
   456  	for i, v := range in {
   457  		v.mustBeExported()
   458  		targ := t.In(i).(*rtype)
   459  		a := uintptr(targ.align)
   460  		off = (off + a - 1) &^ (a - 1)
   461  		n := targ.size
   462  		addr := unsafe.Pointer(uintptr(ptr) + off)
   463  		v = v.assignTo("reflect.Value.Call", targ, (*interface{})(addr))
   464  		if v.flag&flagIndir == 0 {
   465  			storeIword(addr, iword(v.val), n)
   466  		} else {
   467  			memmove(addr, v.val, n)
   468  		}
   469  		off += n
   470  	}
   471  	off = (off + ptrSize - 1) &^ (ptrSize - 1)
   472  
   473  	// Call.
   474  	call(fn, ptr, uint32(size))
   475  
   476  	// Copy return values out of args.
   477  	//
   478  	// TODO(rsc): revisit like above.
   479  	ret := make([]Value, nout)
   480  	for i := 0; i < nout; i++ {
   481  		tv := t.Out(i)
   482  		a := uintptr(tv.Align())
   483  		off = (off + a - 1) &^ (a - 1)
   484  		fl := flagIndir | flag(tv.Kind())<<flagKindShift
   485  		ret[i] = Value{tv.common(), unsafe.Pointer(uintptr(ptr) + off), fl}
   486  		off += tv.Size()
   487  	}
   488  
   489  	return ret
   490  }
   491  
   492  // callReflect is the call implementation used by a function
   493  // returned by MakeFunc. In many ways it is the opposite of the
   494  // method Value.call above. The method above converts a call using Values
   495  // into a call of a function with a concrete argument frame, while
   496  // callReflect converts a call of a function with a concrete argument
   497  // frame into a call using Values.
   498  // It is in this file so that it can be next to the call method above.
   499  // The remainder of the MakeFunc implementation is in makefunc.go.
   500  //
   501  // NOTE: This function must be marked as a "wrapper" in the generated code,
   502  // so that the linker can make it work correctly for panic and recover.
   503  // The gc compilers know to do that for the name "reflect.callReflect".
   504  func callReflect(ctxt *makeFuncImpl, frame unsafe.Pointer) {
   505  	ftyp := ctxt.typ
   506  	f := ctxt.fn
   507  
   508  	// Copy argument frame into Values.
   509  	ptr := frame
   510  	off := uintptr(0)
   511  	in := make([]Value, 0, len(ftyp.in))
   512  	for _, arg := range ftyp.in {
   513  		typ := arg
   514  		off += -off & uintptr(typ.align-1)
   515  		v := Value{typ, nil, flag(typ.Kind()) << flagKindShift}
   516  		if typ.size <= ptrSize {
   517  			// value fits in word.
   518  			v.val = unsafe.Pointer(loadIword(unsafe.Pointer(uintptr(ptr)+off), typ.size))
   519  		} else {
   520  			// value does not fit in word.
   521  			// Must make a copy, because f might keep a reference to it,
   522  			// and we cannot let f keep a reference to the stack frame
   523  			// after this function returns, not even a read-only reference.
   524  			v.val = unsafe_New(typ)
   525  			memmove(v.val, unsafe.Pointer(uintptr(ptr)+off), typ.size)
   526  			v.flag |= flagIndir
   527  		}
   528  		in = append(in, v)
   529  		off += typ.size
   530  	}
   531  
   532  	// Call underlying function.
   533  	out := f(in)
   534  	if len(out) != len(ftyp.out) {
   535  		panic("reflect: wrong return count from function created by MakeFunc")
   536  	}
   537  
   538  	// Copy results back into argument frame.
   539  	if len(ftyp.out) > 0 {
   540  		off += -off & (ptrSize - 1)
   541  		for i, arg := range ftyp.out {
   542  			typ := arg
   543  			v := out[i]
   544  			if v.typ != typ {
   545  				panic("reflect: function created by MakeFunc using " + funcName(f) +
   546  					" returned wrong type: have " +
   547  					out[i].typ.String() + " for " + typ.String())
   548  			}
   549  			if v.flag&flagRO != 0 {
   550  				panic("reflect: function created by MakeFunc using " + funcName(f) +
   551  					" returned value obtained from unexported field")
   552  			}
   553  			off += -off & uintptr(typ.align-1)
   554  			addr := unsafe.Pointer(uintptr(ptr) + off)
   555  			if v.flag&flagIndir == 0 {
   556  				storeIword(addr, iword(v.val), typ.size)
   557  			} else {
   558  				memmove(addr, v.val, typ.size)
   559  			}
   560  			off += typ.size
   561  		}
   562  	}
   563  }
   564  
   565  // methodReceiver returns information about the receiver
   566  // described by v. The Value v may or may not have the
   567  // flagMethod bit set, so the kind cached in v.flag should
   568  // not be used.
   569  func methodReceiver(op string, v Value, methodIndex int) (t *rtype, fn unsafe.Pointer, rcvr iword) {
   570  	i := methodIndex
   571  	if v.typ.Kind() == Interface {
   572  		tt := (*interfaceType)(unsafe.Pointer(v.typ))
   573  		if i < 0 || i >= len(tt.methods) {
   574  			panic("reflect: internal error: invalid method index")
   575  		}
   576  		m := &tt.methods[i]
   577  		if m.pkgPath != nil {
   578  			panic("reflect: " + op + " of unexported method")
   579  		}
   580  		t = m.typ
   581  		iface := (*nonEmptyInterface)(v.val)
   582  		if iface.itab == nil {
   583  			panic("reflect: " + op + " of method on nil interface value")
   584  		}
   585  		fn = unsafe.Pointer(&iface.itab.fun[i])
   586  		rcvr = iface.word
   587  	} else {
   588  		ut := v.typ.uncommon()
   589  		if ut == nil || i < 0 || i >= len(ut.methods) {
   590  			panic("reflect: internal error: invalid method index")
   591  		}
   592  		m := &ut.methods[i]
   593  		if m.pkgPath != nil {
   594  			panic("reflect: " + op + " of unexported method")
   595  		}
   596  		fn = unsafe.Pointer(&m.ifn)
   597  		t = m.mtyp
   598  		rcvr = v.iword()
   599  	}
   600  	return
   601  }
   602  
   603  // align returns the result of rounding x up to a multiple of n.
   604  // n must be a power of two.
   605  func align(x, n uintptr) uintptr {
   606  	return (x + n - 1) &^ (n - 1)
   607  }
   608  
   609  // frameSize returns the sizes of the argument and result frame
   610  // for a function of the given type. The rcvr bool specifies whether
   611  // a one-word receiver should be included in the total.
   612  func frameSize(t *rtype, rcvr bool) (total, in, outOffset, out uintptr) {
   613  	if rcvr {
   614  		// extra word for receiver interface word
   615  		total += ptrSize
   616  	}
   617  
   618  	nin := t.NumIn()
   619  	in = -total
   620  	for i := 0; i < nin; i++ {
   621  		tv := t.In(i)
   622  		total = align(total, uintptr(tv.Align()))
   623  		total += tv.Size()
   624  	}
   625  	in += total
   626  	total = align(total, ptrSize)
   627  	nout := t.NumOut()
   628  	outOffset = total
   629  	out = -total
   630  	for i := 0; i < nout; i++ {
   631  		tv := t.Out(i)
   632  		total = align(total, uintptr(tv.Align()))
   633  		total += tv.Size()
   634  	}
   635  	out += total
   636  
   637  	// total must be > 0 in order for &args[0] to be valid.
   638  	// the argument copying is going to round it up to
   639  	// a multiple of ptrSize anyway, so make it ptrSize to begin with.
   640  	if total < ptrSize {
   641  		total = ptrSize
   642  	}
   643  
   644  	// round to pointer
   645  	total = align(total, ptrSize)
   646  
   647  	return
   648  }
   649  
   650  // callMethod is the call implementation used by a function returned
   651  // by makeMethodValue (used by v.Method(i).Interface()).
   652  // It is a streamlined version of the usual reflect call: the caller has
   653  // already laid out the argument frame for us, so we don't have
   654  // to deal with individual Values for each argument.
   655  // It is in this file so that it can be next to the two similar functions above.
   656  // The remainder of the makeMethodValue implementation is in makefunc.go.
   657  //
   658  // NOTE: This function must be marked as a "wrapper" in the generated code,
   659  // so that the linker can make it work correctly for panic and recover.
   660  // The gc compilers know to do that for the name "reflect.callMethod".
   661  func callMethod(ctxt *methodValue, frame unsafe.Pointer) {
   662  	t, fn, rcvr := methodReceiver("call", ctxt.rcvr, ctxt.method)
   663  	total, in, outOffset, out := frameSize(t, true)
   664  
   665  	// Copy into args.
   666  	//
   667  	// TODO(rsc): This will need to be updated for any new garbage collector.
   668  	// For now make everything look like a pointer by allocating
   669  	// a []unsafe.Pointer.
   670  	args := make([]unsafe.Pointer, total/ptrSize)
   671  	args[0] = unsafe.Pointer(rcvr)
   672  	base := unsafe.Pointer(&args[0])
   673  	memmove(unsafe.Pointer(uintptr(base)+ptrSize), frame, in)
   674  
   675  	// Call.
   676  	call(fn, unsafe.Pointer(&args[0]), uint32(total))
   677  
   678  	// Copy return values.
   679  	memmove(unsafe.Pointer(uintptr(frame)+outOffset-ptrSize), unsafe.Pointer(uintptr(base)+outOffset), out)
   680  }
   681  
   682  // funcName returns the name of f, for use in error messages.
   683  func funcName(f func([]Value) []Value) string {
   684  	pc := *(*uintptr)(unsafe.Pointer(&f))
   685  	rf := runtime.FuncForPC(pc)
   686  	if rf != nil {
   687  		return rf.Name()
   688  	}
   689  	return "closure"
   690  }
   691  
   692  // Cap returns v's capacity.
   693  // It panics if v's Kind is not Array, Chan, or Slice.
   694  func (v Value) Cap() int {
   695  	k := v.kind()
   696  	switch k {
   697  	case Array:
   698  		return v.typ.Len()
   699  	case Chan:
   700  		return int(chancap(v.iword()))
   701  	case Slice:
   702  		// Slice is always bigger than a word; assume flagIndir.
   703  		return (*SliceHeader)(v.val).Cap
   704  	}
   705  	panic(&ValueError{"reflect.Value.Cap", k})
   706  }
   707  
   708  // Close closes the channel v.
   709  // It panics if v's Kind is not Chan.
   710  func (v Value) Close() {
   711  	v.mustBe(Chan)
   712  	v.mustBeExported()
   713  	chanclose(v.iword())
   714  }
   715  
   716  // Complex returns v's underlying value, as a complex128.
   717  // It panics if v's Kind is not Complex64 or Complex128
   718  func (v Value) Complex() complex128 {
   719  	k := v.kind()
   720  	switch k {
   721  	case Complex64:
   722  		if v.flag&flagIndir != 0 {
   723  			return complex128(*(*complex64)(v.val))
   724  		}
   725  		return complex128(*(*complex64)(unsafe.Pointer(&v.val)))
   726  	case Complex128:
   727  		// complex128 is always bigger than a word; assume flagIndir.
   728  		return *(*complex128)(v.val)
   729  	}
   730  	panic(&ValueError{"reflect.Value.Complex", k})
   731  }
   732  
   733  // Elem returns the value that the interface v contains
   734  // or that the pointer v points to.
   735  // It panics if v's Kind is not Interface or Ptr.
   736  // It returns the zero Value if v is nil.
   737  func (v Value) Elem() Value {
   738  	k := v.kind()
   739  	switch k {
   740  	case Interface:
   741  		var (
   742  			typ *rtype
   743  			val unsafe.Pointer
   744  		)
   745  		if v.typ.NumMethod() == 0 {
   746  			eface := (*emptyInterface)(v.val)
   747  			if eface.typ == nil {
   748  				// nil interface value
   749  				return Value{}
   750  			}
   751  			typ = eface.typ
   752  			val = unsafe.Pointer(eface.word)
   753  		} else {
   754  			iface := (*nonEmptyInterface)(v.val)
   755  			if iface.itab == nil {
   756  				// nil interface value
   757  				return Value{}
   758  			}
   759  			typ = iface.itab.typ
   760  			val = unsafe.Pointer(iface.word)
   761  		}
   762  		fl := v.flag & flagRO
   763  		fl |= flag(typ.Kind()) << flagKindShift
   764  		if typ.size > ptrSize {
   765  			fl |= flagIndir
   766  		}
   767  		return Value{typ, val, fl}
   768  
   769  	case Ptr:
   770  		val := v.val
   771  		if v.flag&flagIndir != 0 {
   772  			val = *(*unsafe.Pointer)(val)
   773  		}
   774  		// The returned value's address is v's value.
   775  		if val == nil {
   776  			return Value{}
   777  		}
   778  		tt := (*ptrType)(unsafe.Pointer(v.typ))
   779  		typ := tt.elem
   780  		fl := v.flag&flagRO | flagIndir | flagAddr
   781  		fl |= flag(typ.Kind() << flagKindShift)
   782  		return Value{typ, val, fl}
   783  	}
   784  	panic(&ValueError{"reflect.Value.Elem", k})
   785  }
   786  
   787  // Field returns the i'th field of the struct v.
   788  // It panics if v's Kind is not Struct or i is out of range.
   789  func (v Value) Field(i int) Value {
   790  	v.mustBe(Struct)
   791  	tt := (*structType)(unsafe.Pointer(v.typ))
   792  	if i < 0 || i >= len(tt.fields) {
   793  		panic("reflect: Field index out of range")
   794  	}
   795  	field := &tt.fields[i]
   796  	typ := field.typ
   797  
   798  	// Inherit permission bits from v.
   799  	fl := v.flag & (flagRO | flagIndir | flagAddr)
   800  	// Using an unexported field forces flagRO.
   801  	if field.pkgPath != nil {
   802  		fl |= flagRO
   803  	}
   804  	fl |= flag(typ.Kind()) << flagKindShift
   805  
   806  	var val unsafe.Pointer
   807  	switch {
   808  	case fl&flagIndir != 0:
   809  		// Indirect.  Just bump pointer.
   810  		val = unsafe.Pointer(uintptr(v.val) + field.offset)
   811  	case bigEndian:
   812  		// Direct.  Discard leading bytes.
   813  		val = unsafe.Pointer(uintptr(v.val) << (field.offset * 8))
   814  	default:
   815  		// Direct.  Discard leading bytes.
   816  		val = unsafe.Pointer(uintptr(v.val) >> (field.offset * 8))
   817  	}
   818  
   819  	return Value{typ, val, fl}
   820  }
   821  
   822  // FieldByIndex returns the nested field corresponding to index.
   823  // It panics if v's Kind is not struct.
   824  func (v Value) FieldByIndex(index []int) Value {
   825  	v.mustBe(Struct)
   826  	for i, x := range index {
   827  		if i > 0 {
   828  			if v.Kind() == Ptr && v.Elem().Kind() == Struct {
   829  				v = v.Elem()
   830  			}
   831  		}
   832  		v = v.Field(x)
   833  	}
   834  	return v
   835  }
   836  
   837  // FieldByName returns the struct field with the given name.
   838  // It returns the zero Value if no field was found.
   839  // It panics if v's Kind is not struct.
   840  func (v Value) FieldByName(name string) Value {
   841  	v.mustBe(Struct)
   842  	if f, ok := v.typ.FieldByName(name); ok {
   843  		return v.FieldByIndex(f.Index)
   844  	}
   845  	return Value{}
   846  }
   847  
   848  // FieldByNameFunc returns the struct field with a name
   849  // that satisfies the match function.
   850  // It panics if v's Kind is not struct.
   851  // It returns the zero Value if no field was found.
   852  func (v Value) FieldByNameFunc(match func(string) bool) Value {
   853  	v.mustBe(Struct)
   854  	if f, ok := v.typ.FieldByNameFunc(match); ok {
   855  		return v.FieldByIndex(f.Index)
   856  	}
   857  	return Value{}
   858  }
   859  
   860  // Float returns v's underlying value, as a float64.
   861  // It panics if v's Kind is not Float32 or Float64
   862  func (v Value) Float() float64 {
   863  	k := v.kind()
   864  	switch k {
   865  	case Float32:
   866  		if v.flag&flagIndir != 0 {
   867  			return float64(*(*float32)(v.val))
   868  		}
   869  		return float64(*(*float32)(unsafe.Pointer(&v.val)))
   870  	case Float64:
   871  		if v.flag&flagIndir != 0 {
   872  			return *(*float64)(v.val)
   873  		}
   874  		return *(*float64)(unsafe.Pointer(&v.val))
   875  	}
   876  	panic(&ValueError{"reflect.Value.Float", k})
   877  }
   878  
   879  var uint8Type = TypeOf(uint8(0)).(*rtype)
   880  
   881  // Index returns v's i'th element.
   882  // It panics if v's Kind is not Array, Slice, or String or i is out of range.
   883  func (v Value) Index(i int) Value {
   884  	k := v.kind()
   885  	switch k {
   886  	case Array:
   887  		tt := (*arrayType)(unsafe.Pointer(v.typ))
   888  		if i < 0 || i > int(tt.len) {
   889  			panic("reflect: array index out of range")
   890  		}
   891  		typ := tt.elem
   892  		fl := v.flag & (flagRO | flagIndir | flagAddr) // bits same as overall array
   893  		fl |= flag(typ.Kind()) << flagKindShift
   894  		offset := uintptr(i) * typ.size
   895  
   896  		var val unsafe.Pointer
   897  		switch {
   898  		case fl&flagIndir != 0:
   899  			// Indirect.  Just bump pointer.
   900  			val = unsafe.Pointer(uintptr(v.val) + offset)
   901  		case bigEndian:
   902  			// Direct.  Discard leading bytes.
   903  			val = unsafe.Pointer(uintptr(v.val) << (offset * 8))
   904  		default:
   905  			// Direct.  Discard leading bytes.
   906  			val = unsafe.Pointer(uintptr(v.val) >> (offset * 8))
   907  		}
   908  		return Value{typ, val, fl}
   909  
   910  	case Slice:
   911  		// Element flag same as Elem of Ptr.
   912  		// Addressable, indirect, possibly read-only.
   913  		fl := flagAddr | flagIndir | v.flag&flagRO
   914  		s := (*SliceHeader)(v.val)
   915  		if i < 0 || i >= s.Len {
   916  			panic("reflect: slice index out of range")
   917  		}
   918  		tt := (*sliceType)(unsafe.Pointer(v.typ))
   919  		typ := tt.elem
   920  		fl |= flag(typ.Kind()) << flagKindShift
   921  		val := unsafe.Pointer(s.Data + uintptr(i)*typ.size)
   922  		return Value{typ, val, fl}
   923  
   924  	case String:
   925  		fl := v.flag&flagRO | flag(Uint8<<flagKindShift)
   926  		s := (*StringHeader)(v.val)
   927  		if i < 0 || i >= s.Len {
   928  			panic("reflect: string index out of range")
   929  		}
   930  		val := *(*byte)(unsafe.Pointer(s.Data + uintptr(i)))
   931  		return Value{uint8Type, unsafe.Pointer(uintptr(val)), fl}
   932  	}
   933  	panic(&ValueError{"reflect.Value.Index", k})
   934  }
   935  
   936  // Int returns v's underlying value, as an int64.
   937  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.
   938  func (v Value) Int() int64 {
   939  	k := v.kind()
   940  	var p unsafe.Pointer
   941  	if v.flag&flagIndir != 0 {
   942  		p = v.val
   943  	} else {
   944  		// The escape analysis is good enough that &v.val
   945  		// does not trigger a heap allocation.
   946  		p = unsafe.Pointer(&v.val)
   947  	}
   948  	switch k {
   949  	case Int:
   950  		return int64(*(*int)(p))
   951  	case Int8:
   952  		return int64(*(*int8)(p))
   953  	case Int16:
   954  		return int64(*(*int16)(p))
   955  	case Int32:
   956  		return int64(*(*int32)(p))
   957  	case Int64:
   958  		return int64(*(*int64)(p))
   959  	}
   960  	panic(&ValueError{"reflect.Value.Int", k})
   961  }
   962  
   963  // CanInterface returns true if Interface can be used without panicking.
   964  func (v Value) CanInterface() bool {
   965  	if v.flag == 0 {
   966  		panic(&ValueError{"reflect.Value.CanInterface", Invalid})
   967  	}
   968  	return v.flag&flagRO == 0
   969  }
   970  
   971  // Interface returns v's current value as an interface{}.
   972  // It is equivalent to:
   973  //	var i interface{} = (v's underlying value)
   974  // It panics if the Value was obtained by accessing
   975  // unexported struct fields.
   976  func (v Value) Interface() (i interface{}) {
   977  	return valueInterface(v, true)
   978  }
   979  
   980  func valueInterface(v Value, safe bool) interface{} {
   981  	if v.flag == 0 {
   982  		panic(&ValueError{"reflect.Value.Interface", 0})
   983  	}
   984  	if safe && v.flag&flagRO != 0 {
   985  		// Do not allow access to unexported values via Interface,
   986  		// because they might be pointers that should not be
   987  		// writable or methods or function that should not be callable.
   988  		panic("reflect.Value.Interface: cannot return value obtained from unexported field or method")
   989  	}
   990  	if v.flag&flagMethod != 0 {
   991  		v = makeMethodValue("Interface", v)
   992  	}
   993  
   994  	k := v.kind()
   995  	if k == Interface {
   996  		// Special case: return the element inside the interface.
   997  		// Empty interface has one layout, all interfaces with
   998  		// methods have a second layout.
   999  		if v.NumMethod() == 0 {
  1000  			return *(*interface{})(v.val)
  1001  		}
  1002  		return *(*interface {
  1003  			M()
  1004  		})(v.val)
  1005  	}
  1006  
  1007  	// Non-interface value.
  1008  	var eface emptyInterface
  1009  	eface.typ = v.typ
  1010  	eface.word = v.iword()
  1011  
  1012  	// Don't need to allocate if v is not addressable or fits in one word.
  1013  	if v.flag&flagAddr != 0 && v.typ.size > ptrSize {
  1014  		// eface.word is a pointer to the actual data,
  1015  		// which might be changed.  We need to return
  1016  		// a pointer to unchanging data, so make a copy.
  1017  		ptr := unsafe_New(v.typ)
  1018  		memmove(ptr, unsafe.Pointer(eface.word), v.typ.size)
  1019  		eface.word = iword(ptr)
  1020  	}
  1021  
  1022  	return *(*interface{})(unsafe.Pointer(&eface))
  1023  }
  1024  
  1025  // InterfaceData returns the interface v's value as a uintptr pair.
  1026  // It panics if v's Kind is not Interface.
  1027  func (v Value) InterfaceData() [2]uintptr {
  1028  	v.mustBe(Interface)
  1029  	// We treat this as a read operation, so we allow
  1030  	// it even for unexported data, because the caller
  1031  	// has to import "unsafe" to turn it into something
  1032  	// that can be abused.
  1033  	// Interface value is always bigger than a word; assume flagIndir.
  1034  	return *(*[2]uintptr)(v.val)
  1035  }
  1036  
  1037  // IsNil returns true if v is a nil value.
  1038  // It panics if v's Kind is not Chan, Func, Interface, Map, Ptr, or Slice.
  1039  func (v Value) IsNil() bool {
  1040  	k := v.kind()
  1041  	switch k {
  1042  	case Chan, Func, Map, Ptr:
  1043  		if v.flag&flagMethod != 0 {
  1044  			return false
  1045  		}
  1046  		ptr := v.val
  1047  		if v.flag&flagIndir != 0 {
  1048  			ptr = *(*unsafe.Pointer)(ptr)
  1049  		}
  1050  		return ptr == nil
  1051  	case Interface, Slice:
  1052  		// Both interface and slice are nil if first word is 0.
  1053  		// Both are always bigger than a word; assume flagIndir.
  1054  		return *(*unsafe.Pointer)(v.val) == nil
  1055  	}
  1056  	panic(&ValueError{"reflect.Value.IsNil", k})
  1057  }
  1058  
  1059  // IsValid returns true if v represents a value.
  1060  // It returns false if v is the zero Value.
  1061  // If IsValid returns false, all other methods except String panic.
  1062  // Most functions and methods never return an invalid value.
  1063  // If one does, its documentation states the conditions explicitly.
  1064  func (v Value) IsValid() bool {
  1065  	return v.flag != 0
  1066  }
  1067  
  1068  // Kind returns v's Kind.
  1069  // If v is the zero Value (IsValid returns false), Kind returns Invalid.
  1070  func (v Value) Kind() Kind {
  1071  	return v.kind()
  1072  }
  1073  
  1074  // Len returns v's length.
  1075  // It panics if v's Kind is not Array, Chan, Map, Slice, or String.
  1076  func (v Value) Len() int {
  1077  	k := v.kind()
  1078  	switch k {
  1079  	case Array:
  1080  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1081  		return int(tt.len)
  1082  	case Chan:
  1083  		return chanlen(v.iword())
  1084  	case Map:
  1085  		return maplen(v.iword())
  1086  	case Slice:
  1087  		// Slice is bigger than a word; assume flagIndir.
  1088  		return (*SliceHeader)(v.val).Len
  1089  	case String:
  1090  		// String is bigger than a word; assume flagIndir.
  1091  		return (*StringHeader)(v.val).Len
  1092  	}
  1093  	panic(&ValueError{"reflect.Value.Len", k})
  1094  }
  1095  
  1096  // MapIndex returns the value associated with key in the map v.
  1097  // It panics if v's Kind is not Map.
  1098  // It returns the zero Value if key is not found in the map or if v represents a nil map.
  1099  // As in Go, the key's value must be assignable to the map's key type.
  1100  func (v Value) MapIndex(key Value) Value {
  1101  	v.mustBe(Map)
  1102  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1103  
  1104  	// Do not require key to be exported, so that DeepEqual
  1105  	// and other programs can use all the keys returned by
  1106  	// MapKeys as arguments to MapIndex.  If either the map
  1107  	// or the key is unexported, though, the result will be
  1108  	// considered unexported.  This is consistent with the
  1109  	// behavior for structs, which allow read but not write
  1110  	// of unexported fields.
  1111  	key = key.assignTo("reflect.Value.MapIndex", tt.key, nil)
  1112  
  1113  	word, ok := mapaccess(v.typ, v.iword(), key.iword())
  1114  	if !ok {
  1115  		return Value{}
  1116  	}
  1117  	typ := tt.elem
  1118  	fl := (v.flag | key.flag) & flagRO
  1119  	if typ.size > ptrSize {
  1120  		fl |= flagIndir
  1121  	}
  1122  	fl |= flag(typ.Kind()) << flagKindShift
  1123  	return Value{typ, unsafe.Pointer(word), fl}
  1124  }
  1125  
  1126  // MapKeys returns a slice containing all the keys present in the map,
  1127  // in unspecified order.
  1128  // It panics if v's Kind is not Map.
  1129  // It returns an empty slice if v represents a nil map.
  1130  func (v Value) MapKeys() []Value {
  1131  	v.mustBe(Map)
  1132  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1133  	keyType := tt.key
  1134  
  1135  	fl := v.flag & flagRO
  1136  	fl |= flag(keyType.Kind()) << flagKindShift
  1137  	if keyType.size > ptrSize {
  1138  		fl |= flagIndir
  1139  	}
  1140  
  1141  	m := v.iword()
  1142  	mlen := int(0)
  1143  	if m != nil {
  1144  		mlen = maplen(m)
  1145  	}
  1146  	it := mapiterinit(v.typ, m)
  1147  	a := make([]Value, mlen)
  1148  	var i int
  1149  	for i = 0; i < len(a); i++ {
  1150  		keyWord, ok := mapiterkey(it)
  1151  		if !ok {
  1152  			break
  1153  		}
  1154  		a[i] = Value{keyType, unsafe.Pointer(keyWord), fl}
  1155  		mapiternext(it)
  1156  	}
  1157  	return a[:i]
  1158  }
  1159  
  1160  // Method returns a function value corresponding to v's i'th method.
  1161  // The arguments to a Call on the returned function should not include
  1162  // a receiver; the returned function will always use v as the receiver.
  1163  // Method panics if i is out of range or if v is a nil interface value.
  1164  func (v Value) Method(i int) Value {
  1165  	if v.typ == nil {
  1166  		panic(&ValueError{"reflect.Value.Method", Invalid})
  1167  	}
  1168  	if v.flag&flagMethod != 0 || i < 0 || i >= v.typ.NumMethod() {
  1169  		panic("reflect: Method index out of range")
  1170  	}
  1171  	if v.typ.Kind() == Interface && v.IsNil() {
  1172  		panic("reflect: Method on nil interface value")
  1173  	}
  1174  	fl := v.flag & (flagRO | flagIndir)
  1175  	fl |= flag(Func) << flagKindShift
  1176  	fl |= flag(i)<<flagMethodShift | flagMethod
  1177  	return Value{v.typ, v.val, fl}
  1178  }
  1179  
  1180  // NumMethod returns the number of methods in the value's method set.
  1181  func (v Value) NumMethod() int {
  1182  	if v.typ == nil {
  1183  		panic(&ValueError{"reflect.Value.NumMethod", Invalid})
  1184  	}
  1185  	if v.flag&flagMethod != 0 {
  1186  		return 0
  1187  	}
  1188  	return v.typ.NumMethod()
  1189  }
  1190  
  1191  // MethodByName returns a function value corresponding to the method
  1192  // of v with the given name.
  1193  // The arguments to a Call on the returned function should not include
  1194  // a receiver; the returned function will always use v as the receiver.
  1195  // It returns the zero Value if no method was found.
  1196  func (v Value) MethodByName(name string) Value {
  1197  	if v.typ == nil {
  1198  		panic(&ValueError{"reflect.Value.MethodByName", Invalid})
  1199  	}
  1200  	if v.flag&flagMethod != 0 {
  1201  		return Value{}
  1202  	}
  1203  	m, ok := v.typ.MethodByName(name)
  1204  	if !ok {
  1205  		return Value{}
  1206  	}
  1207  	return v.Method(m.Index)
  1208  }
  1209  
  1210  // NumField returns the number of fields in the struct v.
  1211  // It panics if v's Kind is not Struct.
  1212  func (v Value) NumField() int {
  1213  	v.mustBe(Struct)
  1214  	tt := (*structType)(unsafe.Pointer(v.typ))
  1215  	return len(tt.fields)
  1216  }
  1217  
  1218  // OverflowComplex returns true if the complex128 x cannot be represented by v's type.
  1219  // It panics if v's Kind is not Complex64 or Complex128.
  1220  func (v Value) OverflowComplex(x complex128) bool {
  1221  	k := v.kind()
  1222  	switch k {
  1223  	case Complex64:
  1224  		return overflowFloat32(real(x)) || overflowFloat32(imag(x))
  1225  	case Complex128:
  1226  		return false
  1227  	}
  1228  	panic(&ValueError{"reflect.Value.OverflowComplex", k})
  1229  }
  1230  
  1231  // OverflowFloat returns true if the float64 x cannot be represented by v's type.
  1232  // It panics if v's Kind is not Float32 or Float64.
  1233  func (v Value) OverflowFloat(x float64) bool {
  1234  	k := v.kind()
  1235  	switch k {
  1236  	case Float32:
  1237  		return overflowFloat32(x)
  1238  	case Float64:
  1239  		return false
  1240  	}
  1241  	panic(&ValueError{"reflect.Value.OverflowFloat", k})
  1242  }
  1243  
  1244  func overflowFloat32(x float64) bool {
  1245  	if x < 0 {
  1246  		x = -x
  1247  	}
  1248  	return math.MaxFloat32 < x && x <= math.MaxFloat64
  1249  }
  1250  
  1251  // OverflowInt returns true if the int64 x cannot be represented by v's type.
  1252  // It panics if v's Kind is not Int, Int8, int16, Int32, or Int64.
  1253  func (v Value) OverflowInt(x int64) bool {
  1254  	k := v.kind()
  1255  	switch k {
  1256  	case Int, Int8, Int16, Int32, Int64:
  1257  		bitSize := v.typ.size * 8
  1258  		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
  1259  		return x != trunc
  1260  	}
  1261  	panic(&ValueError{"reflect.Value.OverflowInt", k})
  1262  }
  1263  
  1264  // OverflowUint returns true if the uint64 x cannot be represented by v's type.
  1265  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
  1266  func (v Value) OverflowUint(x uint64) bool {
  1267  	k := v.kind()
  1268  	switch k {
  1269  	case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64:
  1270  		bitSize := v.typ.size * 8
  1271  		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
  1272  		return x != trunc
  1273  	}
  1274  	panic(&ValueError{"reflect.Value.OverflowUint", k})
  1275  }
  1276  
  1277  // Pointer returns v's value as a uintptr.
  1278  // It returns uintptr instead of unsafe.Pointer so that
  1279  // code using reflect cannot obtain unsafe.Pointers
  1280  // without importing the unsafe package explicitly.
  1281  // It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer.
  1282  //
  1283  // If v's Kind is Func, the returned pointer is an underlying
  1284  // code pointer, but not necessarily enough to identify a
  1285  // single function uniquely. The only guarantee is that the
  1286  // result is zero if and only if v is a nil func Value.
  1287  func (v Value) Pointer() uintptr {
  1288  	k := v.kind()
  1289  	switch k {
  1290  	case Chan, Map, Ptr, UnsafePointer:
  1291  		p := v.val
  1292  		if v.flag&flagIndir != 0 {
  1293  			p = *(*unsafe.Pointer)(p)
  1294  		}
  1295  		return uintptr(p)
  1296  	case Func:
  1297  		if v.flag&flagMethod != 0 {
  1298  			// As the doc comment says, the returned pointer is an
  1299  			// underlying code pointer but not necessarily enough to
  1300  			// identify a single function uniquely. All method expressions
  1301  			// created via reflect have the same underlying code pointer,
  1302  			// so their Pointers are equal. The function used here must
  1303  			// match the one used in makeMethodValue.
  1304  			f := methodValueCall
  1305  			return **(**uintptr)(unsafe.Pointer(&f))
  1306  		}
  1307  		p := v.val
  1308  		if v.flag&flagIndir != 0 {
  1309  			p = *(*unsafe.Pointer)(p)
  1310  		}
  1311  		// Non-nil func value points at data block.
  1312  		// First word of data block is actual code.
  1313  		if p != nil {
  1314  			p = *(*unsafe.Pointer)(p)
  1315  		}
  1316  		return uintptr(p)
  1317  
  1318  	case Slice:
  1319  		return (*SliceHeader)(v.val).Data
  1320  	}
  1321  	panic(&ValueError{"reflect.Value.Pointer", k})
  1322  }
  1323  
  1324  // Recv receives and returns a value from the channel v.
  1325  // It panics if v's Kind is not Chan.
  1326  // The receive blocks until a value is ready.
  1327  // The boolean value ok is true if the value x corresponds to a send
  1328  // on the channel, false if it is a zero value received because the channel is closed.
  1329  func (v Value) Recv() (x Value, ok bool) {
  1330  	v.mustBe(Chan)
  1331  	v.mustBeExported()
  1332  	return v.recv(false)
  1333  }
  1334  
  1335  // internal recv, possibly non-blocking (nb).
  1336  // v is known to be a channel.
  1337  func (v Value) recv(nb bool) (val Value, ok bool) {
  1338  	tt := (*chanType)(unsafe.Pointer(v.typ))
  1339  	if ChanDir(tt.dir)&RecvDir == 0 {
  1340  		panic("reflect: recv on send-only channel")
  1341  	}
  1342  	word, selected, ok := chanrecv(v.typ, v.iword(), nb)
  1343  	if selected {
  1344  		typ := tt.elem
  1345  		fl := flag(typ.Kind()) << flagKindShift
  1346  		if typ.size > ptrSize {
  1347  			fl |= flagIndir
  1348  		}
  1349  		val = Value{typ, unsafe.Pointer(word), fl}
  1350  	}
  1351  	return
  1352  }
  1353  
  1354  // Send sends x on the channel v.
  1355  // It panics if v's kind is not Chan or if x's type is not the same type as v's element type.
  1356  // As in Go, x's value must be assignable to the channel's element type.
  1357  func (v Value) Send(x Value) {
  1358  	v.mustBe(Chan)
  1359  	v.mustBeExported()
  1360  	v.send(x, false)
  1361  }
  1362  
  1363  // internal send, possibly non-blocking.
  1364  // v is known to be a channel.
  1365  func (v Value) send(x Value, nb bool) (selected bool) {
  1366  	tt := (*chanType)(unsafe.Pointer(v.typ))
  1367  	if ChanDir(tt.dir)&SendDir == 0 {
  1368  		panic("reflect: send on recv-only channel")
  1369  	}
  1370  	x.mustBeExported()
  1371  	x = x.assignTo("reflect.Value.Send", tt.elem, nil)
  1372  	return chansend(v.typ, v.iword(), x.iword(), nb)
  1373  }
  1374  
  1375  // Set assigns x to the value v.
  1376  // It panics if CanSet returns false.
  1377  // As in Go, x's value must be assignable to v's type.
  1378  func (v Value) Set(x Value) {
  1379  	v.mustBeAssignable()
  1380  	x.mustBeExported() // do not let unexported x leak
  1381  	var target *interface{}
  1382  	if v.kind() == Interface {
  1383  		target = (*interface{})(v.val)
  1384  	}
  1385  	x = x.assignTo("reflect.Set", v.typ, target)
  1386  	if x.flag&flagIndir != 0 {
  1387  		memmove(v.val, x.val, v.typ.size)
  1388  	} else {
  1389  		storeIword(v.val, iword(x.val), v.typ.size)
  1390  	}
  1391  }
  1392  
  1393  // SetBool sets v's underlying value.
  1394  // It panics if v's Kind is not Bool or if CanSet() is false.
  1395  func (v Value) SetBool(x bool) {
  1396  	v.mustBeAssignable()
  1397  	v.mustBe(Bool)
  1398  	*(*bool)(v.val) = x
  1399  }
  1400  
  1401  // SetBytes sets v's underlying value.
  1402  // It panics if v's underlying value is not a slice of bytes.
  1403  func (v Value) SetBytes(x []byte) {
  1404  	v.mustBeAssignable()
  1405  	v.mustBe(Slice)
  1406  	if v.typ.Elem().Kind() != Uint8 {
  1407  		panic("reflect.Value.SetBytes of non-byte slice")
  1408  	}
  1409  	*(*[]byte)(v.val) = x
  1410  }
  1411  
  1412  // setRunes sets v's underlying value.
  1413  // It panics if v's underlying value is not a slice of runes (int32s).
  1414  func (v Value) setRunes(x []rune) {
  1415  	v.mustBeAssignable()
  1416  	v.mustBe(Slice)
  1417  	if v.typ.Elem().Kind() != Int32 {
  1418  		panic("reflect.Value.setRunes of non-rune slice")
  1419  	}
  1420  	*(*[]rune)(v.val) = x
  1421  }
  1422  
  1423  // SetComplex sets v's underlying value to x.
  1424  // It panics if v's Kind is not Complex64 or Complex128, or if CanSet() is false.
  1425  func (v Value) SetComplex(x complex128) {
  1426  	v.mustBeAssignable()
  1427  	switch k := v.kind(); k {
  1428  	default:
  1429  		panic(&ValueError{"reflect.Value.SetComplex", k})
  1430  	case Complex64:
  1431  		*(*complex64)(v.val) = complex64(x)
  1432  	case Complex128:
  1433  		*(*complex128)(v.val) = x
  1434  	}
  1435  }
  1436  
  1437  // SetFloat sets v's underlying value to x.
  1438  // It panics if v's Kind is not Float32 or Float64, or if CanSet() is false.
  1439  func (v Value) SetFloat(x float64) {
  1440  	v.mustBeAssignable()
  1441  	switch k := v.kind(); k {
  1442  	default:
  1443  		panic(&ValueError{"reflect.Value.SetFloat", k})
  1444  	case Float32:
  1445  		*(*float32)(v.val) = float32(x)
  1446  	case Float64:
  1447  		*(*float64)(v.val) = x
  1448  	}
  1449  }
  1450  
  1451  // SetInt sets v's underlying value to x.
  1452  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64, or if CanSet() is false.
  1453  func (v Value) SetInt(x int64) {
  1454  	v.mustBeAssignable()
  1455  	switch k := v.kind(); k {
  1456  	default:
  1457  		panic(&ValueError{"reflect.Value.SetInt", k})
  1458  	case Int:
  1459  		*(*int)(v.val) = int(x)
  1460  	case Int8:
  1461  		*(*int8)(v.val) = int8(x)
  1462  	case Int16:
  1463  		*(*int16)(v.val) = int16(x)
  1464  	case Int32:
  1465  		*(*int32)(v.val) = int32(x)
  1466  	case Int64:
  1467  		*(*int64)(v.val) = x
  1468  	}
  1469  }
  1470  
  1471  // SetLen sets v's length to n.
  1472  // It panics if v's Kind is not Slice or if n is negative or
  1473  // greater than the capacity of the slice.
  1474  func (v Value) SetLen(n int) {
  1475  	v.mustBeAssignable()
  1476  	v.mustBe(Slice)
  1477  	s := (*SliceHeader)(v.val)
  1478  	if n < 0 || n > int(s.Cap) {
  1479  		panic("reflect: slice length out of range in SetLen")
  1480  	}
  1481  	s.Len = n
  1482  }
  1483  
  1484  // SetCap sets v's capacity to n.
  1485  // It panics if v's Kind is not Slice or if n is smaller than the length or
  1486  // greater than the capacity of the slice.
  1487  func (v Value) SetCap(n int) {
  1488  	v.mustBeAssignable()
  1489  	v.mustBe(Slice)
  1490  	s := (*SliceHeader)(v.val)
  1491  	if n < int(s.Len) || n > int(s.Cap) {
  1492  		panic("reflect: slice capacity out of range in SetCap")
  1493  	}
  1494  	s.Cap = n
  1495  }
  1496  
  1497  // SetMapIndex sets the value associated with key in the map v to val.
  1498  // It panics if v's Kind is not Map.
  1499  // If val is the zero Value, SetMapIndex deletes the key from the map.
  1500  // As in Go, key's value must be assignable to the map's key type,
  1501  // and val's value must be assignable to the map's value type.
  1502  func (v Value) SetMapIndex(key, val Value) {
  1503  	v.mustBe(Map)
  1504  	v.mustBeExported()
  1505  	key.mustBeExported()
  1506  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1507  	key = key.assignTo("reflect.Value.SetMapIndex", tt.key, nil)
  1508  	if val.typ != nil {
  1509  		val.mustBeExported()
  1510  		val = val.assignTo("reflect.Value.SetMapIndex", tt.elem, nil)
  1511  	}
  1512  	mapassign(v.typ, v.iword(), key.iword(), val.iword(), val.typ != nil)
  1513  }
  1514  
  1515  // SetUint sets v's underlying value to x.
  1516  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64, or if CanSet() is false.
  1517  func (v Value) SetUint(x uint64) {
  1518  	v.mustBeAssignable()
  1519  	switch k := v.kind(); k {
  1520  	default:
  1521  		panic(&ValueError{"reflect.Value.SetUint", k})
  1522  	case Uint:
  1523  		*(*uint)(v.val) = uint(x)
  1524  	case Uint8:
  1525  		*(*uint8)(v.val) = uint8(x)
  1526  	case Uint16:
  1527  		*(*uint16)(v.val) = uint16(x)
  1528  	case Uint32:
  1529  		*(*uint32)(v.val) = uint32(x)
  1530  	case Uint64:
  1531  		*(*uint64)(v.val) = x
  1532  	case Uintptr:
  1533  		*(*uintptr)(v.val) = uintptr(x)
  1534  	}
  1535  }
  1536  
  1537  // SetPointer sets the unsafe.Pointer value v to x.
  1538  // It panics if v's Kind is not UnsafePointer.
  1539  func (v Value) SetPointer(x unsafe.Pointer) {
  1540  	v.mustBeAssignable()
  1541  	v.mustBe(UnsafePointer)
  1542  	*(*unsafe.Pointer)(v.val) = x
  1543  }
  1544  
  1545  // SetString sets v's underlying value to x.
  1546  // It panics if v's Kind is not String or if CanSet() is false.
  1547  func (v Value) SetString(x string) {
  1548  	v.mustBeAssignable()
  1549  	v.mustBe(String)
  1550  	*(*string)(v.val) = x
  1551  }
  1552  
  1553  // Slice returns v[i:j].
  1554  // It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array,
  1555  // or if the indexes are out of bounds.
  1556  func (v Value) Slice(i, j int) Value {
  1557  	var (
  1558  		cap  int
  1559  		typ  *sliceType
  1560  		base unsafe.Pointer
  1561  	)
  1562  	switch kind := v.kind(); kind {
  1563  	default:
  1564  		panic(&ValueError{"reflect.Value.Slice", kind})
  1565  
  1566  	case Array:
  1567  		if v.flag&flagAddr == 0 {
  1568  			panic("reflect.Value.Slice: slice of unaddressable array")
  1569  		}
  1570  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1571  		cap = int(tt.len)
  1572  		typ = (*sliceType)(unsafe.Pointer(tt.slice))
  1573  		base = v.val
  1574  
  1575  	case Slice:
  1576  		typ = (*sliceType)(unsafe.Pointer(v.typ))
  1577  		s := (*SliceHeader)(v.val)
  1578  		base = unsafe.Pointer(s.Data)
  1579  		cap = s.Cap
  1580  
  1581  	case String:
  1582  		s := (*StringHeader)(v.val)
  1583  		if i < 0 || j < i || j > s.Len {
  1584  			panic("reflect.Value.Slice: string slice index out of bounds")
  1585  		}
  1586  		var x string
  1587  		val := (*StringHeader)(unsafe.Pointer(&x))
  1588  		val.Data = s.Data + uintptr(i)
  1589  		val.Len = j - i
  1590  		return Value{v.typ, unsafe.Pointer(&x), v.flag}
  1591  	}
  1592  
  1593  	if i < 0 || j < i || j > cap {
  1594  		panic("reflect.Value.Slice: slice index out of bounds")
  1595  	}
  1596  
  1597  	// Declare slice so that gc can see the base pointer in it.
  1598  	var x []unsafe.Pointer
  1599  
  1600  	// Reinterpret as *SliceHeader to edit.
  1601  	s := (*SliceHeader)(unsafe.Pointer(&x))
  1602  	s.Data = uintptr(base) + uintptr(i)*typ.elem.Size()
  1603  	s.Len = j - i
  1604  	s.Cap = cap - i
  1605  
  1606  	fl := v.flag&flagRO | flagIndir | flag(Slice)<<flagKindShift
  1607  	return Value{typ.common(), unsafe.Pointer(&x), fl}
  1608  }
  1609  
  1610  // Slice3 is the 3-index form of the slice operation: it returns v[i:j:k].
  1611  // It panics if v's Kind is not Array or Slice, or if v is an unaddressable array,
  1612  // or if the indexes are out of bounds.
  1613  func (v Value) Slice3(i, j, k int) Value {
  1614  	var (
  1615  		cap  int
  1616  		typ  *sliceType
  1617  		base unsafe.Pointer
  1618  	)
  1619  	switch kind := v.kind(); kind {
  1620  	default:
  1621  		panic(&ValueError{"reflect.Value.Slice3", kind})
  1622  
  1623  	case Array:
  1624  		if v.flag&flagAddr == 0 {
  1625  			panic("reflect.Value.Slice: slice of unaddressable array")
  1626  		}
  1627  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1628  		cap = int(tt.len)
  1629  		typ = (*sliceType)(unsafe.Pointer(tt.slice))
  1630  		base = v.val
  1631  
  1632  	case Slice:
  1633  		typ = (*sliceType)(unsafe.Pointer(v.typ))
  1634  		s := (*SliceHeader)(v.val)
  1635  		base = unsafe.Pointer(s.Data)
  1636  		cap = s.Cap
  1637  	}
  1638  
  1639  	if i < 0 || j < i || k < j || k > cap {
  1640  		panic("reflect.Value.Slice3: slice index out of bounds")
  1641  	}
  1642  
  1643  	// Declare slice so that the garbage collector
  1644  	// can see the base pointer in it.
  1645  	var x []unsafe.Pointer
  1646  
  1647  	// Reinterpret as *SliceHeader to edit.
  1648  	s := (*SliceHeader)(unsafe.Pointer(&x))
  1649  	s.Data = uintptr(base) + uintptr(i)*typ.elem.Size()
  1650  	s.Len = j - i
  1651  	s.Cap = k - i
  1652  
  1653  	fl := v.flag&flagRO | flagIndir | flag(Slice)<<flagKindShift
  1654  	return Value{typ.common(), unsafe.Pointer(&x), fl}
  1655  }
  1656  
  1657  // String returns the string v's underlying value, as a string.
  1658  // String is a special case because of Go's String method convention.
  1659  // Unlike the other getters, it does not panic if v's Kind is not String.
  1660  // Instead, it returns a string of the form "<T value>" where T is v's type.
  1661  func (v Value) String() string {
  1662  	switch k := v.kind(); k {
  1663  	case Invalid:
  1664  		return "<invalid Value>"
  1665  	case String:
  1666  		return *(*string)(v.val)
  1667  	}
  1668  	// If you call String on a reflect.Value of other type, it's better to
  1669  	// print something than to panic. Useful in debugging.
  1670  	return "<" + v.typ.String() + " Value>"
  1671  }
  1672  
  1673  // TryRecv attempts to receive a value from the channel v but will not block.
  1674  // It panics if v's Kind is not Chan.
  1675  // If the receive cannot finish without blocking, x is the zero Value.
  1676  // The boolean ok is true if the value x corresponds to a send
  1677  // on the channel, false if it is a zero value received because the channel is closed.
  1678  func (v Value) TryRecv() (x Value, ok bool) {
  1679  	v.mustBe(Chan)
  1680  	v.mustBeExported()
  1681  	return v.recv(true)
  1682  }
  1683  
  1684  // TrySend attempts to send x on the channel v but will not block.
  1685  // It panics if v's Kind is not Chan.
  1686  // It returns true if the value was sent, false otherwise.
  1687  // As in Go, x's value must be assignable to the channel's element type.
  1688  func (v Value) TrySend(x Value) bool {
  1689  	v.mustBe(Chan)
  1690  	v.mustBeExported()
  1691  	return v.send(x, true)
  1692  }
  1693  
  1694  // Type returns v's type.
  1695  func (v Value) Type() Type {
  1696  	f := v.flag
  1697  	if f == 0 {
  1698  		panic(&ValueError{"reflect.Value.Type", Invalid})
  1699  	}
  1700  	if f&flagMethod == 0 {
  1701  		// Easy case
  1702  		return v.typ
  1703  	}
  1704  
  1705  	// Method value.
  1706  	// v.typ describes the receiver, not the method type.
  1707  	i := int(v.flag) >> flagMethodShift
  1708  	if v.typ.Kind() == Interface {
  1709  		// Method on interface.
  1710  		tt := (*interfaceType)(unsafe.Pointer(v.typ))
  1711  		if i < 0 || i >= len(tt.methods) {
  1712  			panic("reflect: internal error: invalid method index")
  1713  		}
  1714  		m := &tt.methods[i]
  1715  		return m.typ
  1716  	}
  1717  	// Method on concrete type.
  1718  	ut := v.typ.uncommon()
  1719  	if ut == nil || i < 0 || i >= len(ut.methods) {
  1720  		panic("reflect: internal error: invalid method index")
  1721  	}
  1722  	m := &ut.methods[i]
  1723  	return m.mtyp
  1724  }
  1725  
  1726  // Uint returns v's underlying value, as a uint64.
  1727  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
  1728  func (v Value) Uint() uint64 {
  1729  	k := v.kind()
  1730  	var p unsafe.Pointer
  1731  	if v.flag&flagIndir != 0 {
  1732  		p = v.val
  1733  	} else {
  1734  		// The escape analysis is good enough that &v.val
  1735  		// does not trigger a heap allocation.
  1736  		p = unsafe.Pointer(&v.val)
  1737  	}
  1738  	switch k {
  1739  	case Uint:
  1740  		return uint64(*(*uint)(p))
  1741  	case Uint8:
  1742  		return uint64(*(*uint8)(p))
  1743  	case Uint16:
  1744  		return uint64(*(*uint16)(p))
  1745  	case Uint32:
  1746  		return uint64(*(*uint32)(p))
  1747  	case Uint64:
  1748  		return uint64(*(*uint64)(p))
  1749  	case Uintptr:
  1750  		return uint64(*(*uintptr)(p))
  1751  	}
  1752  	panic(&ValueError{"reflect.Value.Uint", k})
  1753  }
  1754  
  1755  // UnsafeAddr returns a pointer to v's data.
  1756  // It is for advanced clients that also import the "unsafe" package.
  1757  // It panics if v is not addressable.
  1758  func (v Value) UnsafeAddr() uintptr {
  1759  	if v.typ == nil {
  1760  		panic(&ValueError{"reflect.Value.UnsafeAddr", Invalid})
  1761  	}
  1762  	if v.flag&flagAddr == 0 {
  1763  		panic("reflect.Value.UnsafeAddr of unaddressable value")
  1764  	}
  1765  	return uintptr(v.val)
  1766  }
  1767  
  1768  // StringHeader is the runtime representation of a string.
  1769  // It cannot be used safely or portably and its representation may
  1770  // change in a later release.
  1771  // Moreover, the Data field is not sufficient to guarantee the data
  1772  // it references will not be garbage collected, so programs must keep
  1773  // a separate, correctly typed pointer to the underlying data.
  1774  type StringHeader struct {
  1775  	Data uintptr
  1776  	Len  int
  1777  }
  1778  
  1779  // SliceHeader is the runtime representation of a slice.
  1780  // It cannot be used safely or portably and its representation may
  1781  // change in a later release.
  1782  // Moreover, the Data field is not sufficient to guarantee the data
  1783  // it references will not be garbage collected, so programs must keep
  1784  // a separate, correctly typed pointer to the underlying data.
  1785  type SliceHeader struct {
  1786  	Data uintptr
  1787  	Len  int
  1788  	Cap  int
  1789  }
  1790  
  1791  func typesMustMatch(what string, t1, t2 Type) {
  1792  	if t1 != t2 {
  1793  		panic(what + ": " + t1.String() + " != " + t2.String())
  1794  	}
  1795  }
  1796  
  1797  // grow grows the slice s so that it can hold extra more values, allocating
  1798  // more capacity if needed. It also returns the old and new slice lengths.
  1799  func grow(s Value, extra int) (Value, int, int) {
  1800  	i0 := s.Len()
  1801  	i1 := i0 + extra
  1802  	if i1 < i0 {
  1803  		panic("reflect.Append: slice overflow")
  1804  	}
  1805  	m := s.Cap()
  1806  	if i1 <= m {
  1807  		return s.Slice(0, i1), i0, i1
  1808  	}
  1809  	if m == 0 {
  1810  		m = extra
  1811  	} else {
  1812  		for m < i1 {
  1813  			if i0 < 1024 {
  1814  				m += m
  1815  			} else {
  1816  				m += m / 4
  1817  			}
  1818  		}
  1819  	}
  1820  	t := MakeSlice(s.Type(), i1, m)
  1821  	Copy(t, s)
  1822  	return t, i0, i1
  1823  }
  1824  
  1825  // Append appends the values x to a slice s and returns the resulting slice.
  1826  // As in Go, each x's value must be assignable to the slice's element type.
  1827  func Append(s Value, x ...Value) Value {
  1828  	s.mustBe(Slice)
  1829  	s, i0, i1 := grow(s, len(x))
  1830  	for i, j := i0, 0; i < i1; i, j = i+1, j+1 {
  1831  		s.Index(i).Set(x[j])
  1832  	}
  1833  	return s
  1834  }
  1835  
  1836  // AppendSlice appends a slice t to a slice s and returns the resulting slice.
  1837  // The slices s and t must have the same element type.
  1838  func AppendSlice(s, t Value) Value {
  1839  	s.mustBe(Slice)
  1840  	t.mustBe(Slice)
  1841  	typesMustMatch("reflect.AppendSlice", s.Type().Elem(), t.Type().Elem())
  1842  	s, i0, i1 := grow(s, t.Len())
  1843  	Copy(s.Slice(i0, i1), t)
  1844  	return s
  1845  }
  1846  
  1847  // Copy copies the contents of src into dst until either
  1848  // dst has been filled or src has been exhausted.
  1849  // It returns the number of elements copied.
  1850  // Dst and src each must have kind Slice or Array, and
  1851  // dst and src must have the same element type.
  1852  func Copy(dst, src Value) int {
  1853  	dk := dst.kind()
  1854  	if dk != Array && dk != Slice {
  1855  		panic(&ValueError{"reflect.Copy", dk})
  1856  	}
  1857  	if dk == Array {
  1858  		dst.mustBeAssignable()
  1859  	}
  1860  	dst.mustBeExported()
  1861  
  1862  	sk := src.kind()
  1863  	if sk != Array && sk != Slice {
  1864  		panic(&ValueError{"reflect.Copy", sk})
  1865  	}
  1866  	src.mustBeExported()
  1867  
  1868  	de := dst.typ.Elem()
  1869  	se := src.typ.Elem()
  1870  	typesMustMatch("reflect.Copy", de, se)
  1871  
  1872  	n := dst.Len()
  1873  	if sn := src.Len(); n > sn {
  1874  		n = sn
  1875  	}
  1876  
  1877  	// If sk is an in-line array, cannot take its address.
  1878  	// Instead, copy element by element.
  1879  	if src.flag&flagIndir == 0 {
  1880  		for i := 0; i < n; i++ {
  1881  			dst.Index(i).Set(src.Index(i))
  1882  		}
  1883  		return n
  1884  	}
  1885  
  1886  	// Copy via memmove.
  1887  	var da, sa unsafe.Pointer
  1888  	if dk == Array {
  1889  		da = dst.val
  1890  	} else {
  1891  		da = unsafe.Pointer((*SliceHeader)(dst.val).Data)
  1892  	}
  1893  	if sk == Array {
  1894  		sa = src.val
  1895  	} else {
  1896  		sa = unsafe.Pointer((*SliceHeader)(src.val).Data)
  1897  	}
  1898  	memmove(da, sa, uintptr(n)*de.Size())
  1899  	return n
  1900  }
  1901  
  1902  // A runtimeSelect is a single case passed to rselect.
  1903  // This must match ../runtime/chan.c:/runtimeSelect
  1904  type runtimeSelect struct {
  1905  	dir uintptr // 0, SendDir, or RecvDir
  1906  	typ *rtype  // channel type
  1907  	ch  iword   // interface word for channel
  1908  	val iword   // interface word for value (for SendDir)
  1909  }
  1910  
  1911  // rselect runs a select. It returns the index of the chosen case,
  1912  // and if the case was a receive, the interface word of the received
  1913  // value and the conventional OK bool to indicate whether the receive
  1914  // corresponds to a sent value.
  1915  func rselect([]runtimeSelect) (chosen int, recv iword, recvOK bool)
  1916  
  1917  // A SelectDir describes the communication direction of a select case.
  1918  type SelectDir int
  1919  
  1920  // NOTE: These values must match ../runtime/chan.c:/SelectDir.
  1921  
  1922  const (
  1923  	_             SelectDir = iota
  1924  	SelectSend              // case Chan <- Send
  1925  	SelectRecv              // case <-Chan:
  1926  	SelectDefault           // default
  1927  )
  1928  
  1929  // A SelectCase describes a single case in a select operation.
  1930  // The kind of case depends on Dir, the communication direction.
  1931  //
  1932  // If Dir is SelectDefault, the case represents a default case.
  1933  // Chan and Send must be zero Values.
  1934  //
  1935  // If Dir is SelectSend, the case represents a send operation.
  1936  // Normally Chan's underlying value must be a channel, and Send's underlying value must be
  1937  // assignable to the channel's element type. As a special case, if Chan is a zero Value,
  1938  // then the case is ignored, and the field Send will also be ignored and may be either zero
  1939  // or non-zero.
  1940  //
  1941  // If Dir is SelectRecv, the case represents a receive operation.
  1942  // Normally Chan's underlying value must be a channel and Send must be a zero Value.
  1943  // If Chan is a zero Value, then the case is ignored, but Send must still be a zero Value.
  1944  // When a receive operation is selected, the received Value is returned by Select.
  1945  //
  1946  type SelectCase struct {
  1947  	Dir  SelectDir // direction of case
  1948  	Chan Value     // channel to use (for send or receive)
  1949  	Send Value     // value to send (for send)
  1950  }
  1951  
  1952  // Select executes a select operation described by the list of cases.
  1953  // Like the Go select statement, it blocks until at least one of the cases
  1954  // can proceed, makes a uniform pseudo-random choice,
  1955  // and then executes that case. It returns the index of the chosen case
  1956  // and, if that case was a receive operation, the value received and a
  1957  // boolean indicating whether the value corresponds to a send on the channel
  1958  // (as opposed to a zero value received because the channel is closed).
  1959  func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool) {
  1960  	// NOTE: Do not trust that caller is not modifying cases data underfoot.
  1961  	// The range is safe because the caller cannot modify our copy of the len
  1962  	// and each iteration makes its own copy of the value c.
  1963  	runcases := make([]runtimeSelect, len(cases))
  1964  	haveDefault := false
  1965  	for i, c := range cases {
  1966  		rc := &runcases[i]
  1967  		rc.dir = uintptr(c.Dir)
  1968  		switch c.Dir {
  1969  		default:
  1970  			panic("reflect.Select: invalid Dir")
  1971  
  1972  		case SelectDefault: // default
  1973  			if haveDefault {
  1974  				panic("reflect.Select: multiple default cases")
  1975  			}
  1976  			haveDefault = true
  1977  			if c.Chan.IsValid() {
  1978  				panic("reflect.Select: default case has Chan value")
  1979  			}
  1980  			if c.Send.IsValid() {
  1981  				panic("reflect.Select: default case has Send value")
  1982  			}
  1983  
  1984  		case SelectSend:
  1985  			ch := c.Chan
  1986  			if !ch.IsValid() {
  1987  				break
  1988  			}
  1989  			ch.mustBe(Chan)
  1990  			ch.mustBeExported()
  1991  			tt := (*chanType)(unsafe.Pointer(ch.typ))
  1992  			if ChanDir(tt.dir)&SendDir == 0 {
  1993  				panic("reflect.Select: SendDir case using recv-only channel")
  1994  			}
  1995  			rc.ch = ch.iword()
  1996  			rc.typ = &tt.rtype
  1997  			v := c.Send
  1998  			if !v.IsValid() {
  1999  				panic("reflect.Select: SendDir case missing Send value")
  2000  			}
  2001  			v.mustBeExported()
  2002  			v = v.assignTo("reflect.Select", tt.elem, nil)
  2003  			rc.val = v.iword()
  2004  
  2005  		case SelectRecv:
  2006  			if c.Send.IsValid() {
  2007  				panic("reflect.Select: RecvDir case has Send value")
  2008  			}
  2009  			ch := c.Chan
  2010  			if !ch.IsValid() {
  2011  				break
  2012  			}
  2013  			ch.mustBe(Chan)
  2014  			ch.mustBeExported()
  2015  			tt := (*chanType)(unsafe.Pointer(ch.typ))
  2016  			rc.typ = &tt.rtype
  2017  			if ChanDir(tt.dir)&RecvDir == 0 {
  2018  				panic("reflect.Select: RecvDir case using send-only channel")
  2019  			}
  2020  			rc.ch = ch.iword()
  2021  		}
  2022  	}
  2023  
  2024  	chosen, word, recvOK := rselect(runcases)
  2025  	if runcases[chosen].dir == uintptr(SelectRecv) {
  2026  		tt := (*chanType)(unsafe.Pointer(runcases[chosen].typ))
  2027  		typ := tt.elem
  2028  		fl := flag(typ.Kind()) << flagKindShift
  2029  		if typ.size > ptrSize {
  2030  			fl |= flagIndir
  2031  		}
  2032  		recv = Value{typ, unsafe.Pointer(word), fl}
  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  	// Declare slice so that gc can see the base pointer in it.
  2062  	var x []unsafe.Pointer
  2063  
  2064  	// Reinterpret as *SliceHeader to edit.
  2065  	s := (*SliceHeader)(unsafe.Pointer(&x))
  2066  	s.Data = uintptr(unsafe_NewArray(typ.Elem().(*rtype), cap))
  2067  	s.Len = len
  2068  	s.Cap = cap
  2069  
  2070  	return Value{typ.common(), unsafe.Pointer(&x), flagIndir | flag(Slice)<<flagKindShift}
  2071  }
  2072  
  2073  // MakeChan creates a new channel with the specified type and buffer size.
  2074  func MakeChan(typ Type, buffer int) Value {
  2075  	if typ.Kind() != Chan {
  2076  		panic("reflect.MakeChan of non-chan type")
  2077  	}
  2078  	if buffer < 0 {
  2079  		panic("reflect.MakeChan: negative buffer size")
  2080  	}
  2081  	if typ.ChanDir() != BothDir {
  2082  		panic("reflect.MakeChan: unidirectional channel type")
  2083  	}
  2084  	ch := makechan(typ.(*rtype), uint64(buffer))
  2085  	return Value{typ.common(), unsafe.Pointer(ch), flag(Chan) << flagKindShift}
  2086  }
  2087  
  2088  // MakeMap creates a new map of the specified type.
  2089  func MakeMap(typ Type) Value {
  2090  	if typ.Kind() != Map {
  2091  		panic("reflect.MakeMap of non-map type")
  2092  	}
  2093  	m := makemap(typ.(*rtype))
  2094  	return Value{typ.common(), unsafe.Pointer(m), flag(Map) << flagKindShift}
  2095  }
  2096  
  2097  // Indirect returns the value that v points to.
  2098  // If v is a nil pointer, Indirect returns a zero Value.
  2099  // If v is not a pointer, Indirect returns v.
  2100  func Indirect(v Value) Value {
  2101  	if v.Kind() != Ptr {
  2102  		return v
  2103  	}
  2104  	return v.Elem()
  2105  }
  2106  
  2107  // ValueOf returns a new Value initialized to the concrete value
  2108  // stored in the interface i.  ValueOf(nil) returns the zero Value.
  2109  func ValueOf(i interface{}) Value {
  2110  	if i == nil {
  2111  		return Value{}
  2112  	}
  2113  
  2114  	// TODO(rsc): Eliminate this terrible hack.
  2115  	// In the call to packValue, eface.typ doesn't escape,
  2116  	// and eface.word is an integer.  So it looks like
  2117  	// i (= eface) doesn't escape.  But really it does,
  2118  	// because eface.word is actually a pointer.
  2119  	escapes(i)
  2120  
  2121  	// For an interface value with the noAddr bit set,
  2122  	// the representation is identical to an empty interface.
  2123  	eface := *(*emptyInterface)(unsafe.Pointer(&i))
  2124  	typ := eface.typ
  2125  	fl := flag(typ.Kind()) << flagKindShift
  2126  	if typ.size > ptrSize {
  2127  		fl |= flagIndir
  2128  	}
  2129  	return Value{typ, unsafe.Pointer(eface.word), fl}
  2130  }
  2131  
  2132  // Zero returns a Value representing the zero value for the specified type.
  2133  // The result is different from the zero value of the Value struct,
  2134  // which represents no value at all.
  2135  // For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0.
  2136  // The returned value is neither addressable nor settable.
  2137  func Zero(typ Type) Value {
  2138  	if typ == nil {
  2139  		panic("reflect: Zero(nil)")
  2140  	}
  2141  	t := typ.common()
  2142  	fl := flag(t.Kind()) << flagKindShift
  2143  	if t.size <= ptrSize {
  2144  		return Value{t, nil, fl}
  2145  	}
  2146  	return Value{t, unsafe_New(typ.(*rtype)), fl | flagIndir}
  2147  }
  2148  
  2149  // New returns a Value representing a pointer to a new zero value
  2150  // for the specified type.  That is, the returned Value's Type is PtrTo(t).
  2151  func New(typ Type) Value {
  2152  	if typ == nil {
  2153  		panic("reflect: New(nil)")
  2154  	}
  2155  	ptr := unsafe_New(typ.(*rtype))
  2156  	fl := flag(Ptr) << flagKindShift
  2157  	return Value{typ.common().ptrTo(), ptr, fl}
  2158  }
  2159  
  2160  // NewAt returns a Value representing a pointer to a value of the
  2161  // specified type, using p as that pointer.
  2162  func NewAt(typ Type, p unsafe.Pointer) Value {
  2163  	fl := flag(Ptr) << flagKindShift
  2164  	return Value{typ.common().ptrTo(), p, fl}
  2165  }
  2166  
  2167  // assignTo returns a value v that can be assigned directly to typ.
  2168  // It panics if v is not assignable to typ.
  2169  // For a conversion to an interface type, target is a suggested scratch space to use.
  2170  func (v Value) assignTo(context string, dst *rtype, target *interface{}) Value {
  2171  	if v.flag&flagMethod != 0 {
  2172  		v = makeMethodValue(context, v)
  2173  	}
  2174  
  2175  	switch {
  2176  	case directlyAssignable(dst, v.typ):
  2177  		// Overwrite type so that they match.
  2178  		// Same memory layout, so no harm done.
  2179  		v.typ = dst
  2180  		fl := v.flag & (flagRO | flagAddr | flagIndir)
  2181  		fl |= flag(dst.Kind()) << flagKindShift
  2182  		return Value{dst, v.val, fl}
  2183  
  2184  	case implements(dst, v.typ):
  2185  		if target == nil {
  2186  			target = new(interface{})
  2187  		}
  2188  		x := valueInterface(v, false)
  2189  		if dst.NumMethod() == 0 {
  2190  			*target = x
  2191  		} else {
  2192  			ifaceE2I(dst, x, unsafe.Pointer(target))
  2193  		}
  2194  		return Value{dst, unsafe.Pointer(target), flagIndir | flag(Interface)<<flagKindShift}
  2195  	}
  2196  
  2197  	// Failed.
  2198  	panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String())
  2199  }
  2200  
  2201  // Convert returns the value v converted to type t.
  2202  // If the usual Go conversion rules do not allow conversion
  2203  // of the value v to type t, Convert panics.
  2204  func (v Value) Convert(t Type) Value {
  2205  	if v.flag&flagMethod != 0 {
  2206  		v = makeMethodValue("Convert", v)
  2207  	}
  2208  	op := convertOp(t.common(), v.typ)
  2209  	if op == nil {
  2210  		panic("reflect.Value.Convert: value of type " + v.typ.String() + " cannot be converted to type " + t.String())
  2211  	}
  2212  	return op(v, t)
  2213  }
  2214  
  2215  // convertOp returns the function to convert a value of type src
  2216  // to a value of type dst. If the conversion is illegal, convertOp returns nil.
  2217  func convertOp(dst, src *rtype) func(Value, Type) Value {
  2218  	switch src.Kind() {
  2219  	case Int, Int8, Int16, Int32, Int64:
  2220  		switch dst.Kind() {
  2221  		case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2222  			return cvtInt
  2223  		case Float32, Float64:
  2224  			return cvtIntFloat
  2225  		case String:
  2226  			return cvtIntString
  2227  		}
  2228  
  2229  	case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2230  		switch dst.Kind() {
  2231  		case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2232  			return cvtUint
  2233  		case Float32, Float64:
  2234  			return cvtUintFloat
  2235  		case String:
  2236  			return cvtUintString
  2237  		}
  2238  
  2239  	case Float32, Float64:
  2240  		switch dst.Kind() {
  2241  		case Int, Int8, Int16, Int32, Int64:
  2242  			return cvtFloatInt
  2243  		case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2244  			return cvtFloatUint
  2245  		case Float32, Float64:
  2246  			return cvtFloat
  2247  		}
  2248  
  2249  	case Complex64, Complex128:
  2250  		switch dst.Kind() {
  2251  		case Complex64, Complex128:
  2252  			return cvtComplex
  2253  		}
  2254  
  2255  	case String:
  2256  		if dst.Kind() == Slice && dst.Elem().PkgPath() == "" {
  2257  			switch dst.Elem().Kind() {
  2258  			case Uint8:
  2259  				return cvtStringBytes
  2260  			case Int32:
  2261  				return cvtStringRunes
  2262  			}
  2263  		}
  2264  
  2265  	case Slice:
  2266  		if dst.Kind() == String && src.Elem().PkgPath() == "" {
  2267  			switch src.Elem().Kind() {
  2268  			case Uint8:
  2269  				return cvtBytesString
  2270  			case Int32:
  2271  				return cvtRunesString
  2272  			}
  2273  		}
  2274  	}
  2275  
  2276  	// dst and src have same underlying type.
  2277  	if haveIdenticalUnderlyingType(dst, src) {
  2278  		return cvtDirect
  2279  	}
  2280  
  2281  	// dst and src are unnamed pointer types with same underlying base type.
  2282  	if dst.Kind() == Ptr && dst.Name() == "" &&
  2283  		src.Kind() == Ptr && src.Name() == "" &&
  2284  		haveIdenticalUnderlyingType(dst.Elem().common(), src.Elem().common()) {
  2285  		return cvtDirect
  2286  	}
  2287  
  2288  	if implements(dst, src) {
  2289  		if src.Kind() == Interface {
  2290  			return cvtI2I
  2291  		}
  2292  		return cvtT2I
  2293  	}
  2294  
  2295  	return nil
  2296  }
  2297  
  2298  // makeInt returns a Value of type t equal to bits (possibly truncated),
  2299  // where t is a signed or unsigned int type.
  2300  func makeInt(f flag, bits uint64, t Type) Value {
  2301  	typ := t.common()
  2302  	if typ.size > ptrSize {
  2303  		// Assume ptrSize >= 4, so this must be uint64.
  2304  		ptr := unsafe_New(typ)
  2305  		*(*uint64)(unsafe.Pointer(ptr)) = bits
  2306  		return Value{typ, ptr, f | flagIndir | flag(typ.Kind())<<flagKindShift}
  2307  	}
  2308  	var w iword
  2309  	switch typ.size {
  2310  	case 1:
  2311  		*(*uint8)(unsafe.Pointer(&w)) = uint8(bits)
  2312  	case 2:
  2313  		*(*uint16)(unsafe.Pointer(&w)) = uint16(bits)
  2314  	case 4:
  2315  		*(*uint32)(unsafe.Pointer(&w)) = uint32(bits)
  2316  	case 8:
  2317  		*(*uint64)(unsafe.Pointer(&w)) = uint64(bits)
  2318  	}
  2319  	return Value{typ, unsafe.Pointer(w), f | flag(typ.Kind())<<flagKindShift}
  2320  }
  2321  
  2322  // makeFloat returns a Value of type t equal to v (possibly truncated to float32),
  2323  // where t is a float32 or float64 type.
  2324  func makeFloat(f flag, v float64, t Type) Value {
  2325  	typ := t.common()
  2326  	if typ.size > ptrSize {
  2327  		// Assume ptrSize >= 4, so this must be float64.
  2328  		ptr := unsafe_New(typ)
  2329  		*(*float64)(unsafe.Pointer(ptr)) = v
  2330  		return Value{typ, ptr, f | flagIndir | flag(typ.Kind())<<flagKindShift}
  2331  	}
  2332  
  2333  	var w iword
  2334  	switch typ.size {
  2335  	case 4:
  2336  		*(*float32)(unsafe.Pointer(&w)) = float32(v)
  2337  	case 8:
  2338  		*(*float64)(unsafe.Pointer(&w)) = v
  2339  	}
  2340  	return Value{typ, unsafe.Pointer(w), f | flag(typ.Kind())<<flagKindShift}
  2341  }
  2342  
  2343  // makeComplex returns a Value of type t equal to v (possibly truncated to complex64),
  2344  // where t is a complex64 or complex128 type.
  2345  func makeComplex(f flag, v complex128, t Type) Value {
  2346  	typ := t.common()
  2347  	if typ.size > ptrSize {
  2348  		ptr := unsafe_New(typ)
  2349  		switch typ.size {
  2350  		case 8:
  2351  			*(*complex64)(unsafe.Pointer(ptr)) = complex64(v)
  2352  		case 16:
  2353  			*(*complex128)(unsafe.Pointer(ptr)) = v
  2354  		}
  2355  		return Value{typ, ptr, f | flagIndir | flag(typ.Kind())<<flagKindShift}
  2356  	}
  2357  
  2358  	// Assume ptrSize <= 8 so this must be complex64.
  2359  	var w iword
  2360  	*(*complex64)(unsafe.Pointer(&w)) = complex64(v)
  2361  	return Value{typ, unsafe.Pointer(w), f | flag(typ.Kind())<<flagKindShift}
  2362  }
  2363  
  2364  func makeString(f flag, v string, t Type) Value {
  2365  	ret := New(t).Elem()
  2366  	ret.SetString(v)
  2367  	ret.flag = ret.flag&^flagAddr | f
  2368  	return ret
  2369  }
  2370  
  2371  func makeBytes(f flag, v []byte, t Type) Value {
  2372  	ret := New(t).Elem()
  2373  	ret.SetBytes(v)
  2374  	ret.flag = ret.flag&^flagAddr | f
  2375  	return ret
  2376  }
  2377  
  2378  func makeRunes(f flag, v []rune, t Type) Value {
  2379  	ret := New(t).Elem()
  2380  	ret.setRunes(v)
  2381  	ret.flag = ret.flag&^flagAddr | f
  2382  	return ret
  2383  }
  2384  
  2385  // These conversion functions are returned by convertOp
  2386  // for classes of conversions. For example, the first function, cvtInt,
  2387  // takes any value v of signed int type and returns the value converted
  2388  // to type t, where t is any signed or unsigned int type.
  2389  
  2390  // convertOp: intXX -> [u]intXX
  2391  func cvtInt(v Value, t Type) Value {
  2392  	return makeInt(v.flag&flagRO, uint64(v.Int()), t)
  2393  }
  2394  
  2395  // convertOp: uintXX -> [u]intXX
  2396  func cvtUint(v Value, t Type) Value {
  2397  	return makeInt(v.flag&flagRO, v.Uint(), t)
  2398  }
  2399  
  2400  // convertOp: floatXX -> intXX
  2401  func cvtFloatInt(v Value, t Type) Value {
  2402  	return makeInt(v.flag&flagRO, uint64(int64(v.Float())), t)
  2403  }
  2404  
  2405  // convertOp: floatXX -> uintXX
  2406  func cvtFloatUint(v Value, t Type) Value {
  2407  	return makeInt(v.flag&flagRO, uint64(v.Float()), t)
  2408  }
  2409  
  2410  // convertOp: intXX -> floatXX
  2411  func cvtIntFloat(v Value, t Type) Value {
  2412  	return makeFloat(v.flag&flagRO, float64(v.Int()), t)
  2413  }
  2414  
  2415  // convertOp: uintXX -> floatXX
  2416  func cvtUintFloat(v Value, t Type) Value {
  2417  	return makeFloat(v.flag&flagRO, float64(v.Uint()), t)
  2418  }
  2419  
  2420  // convertOp: floatXX -> floatXX
  2421  func cvtFloat(v Value, t Type) Value {
  2422  	return makeFloat(v.flag&flagRO, v.Float(), t)
  2423  }
  2424  
  2425  // convertOp: complexXX -> complexXX
  2426  func cvtComplex(v Value, t Type) Value {
  2427  	return makeComplex(v.flag&flagRO, v.Complex(), t)
  2428  }
  2429  
  2430  // convertOp: intXX -> string
  2431  func cvtIntString(v Value, t Type) Value {
  2432  	return makeString(v.flag&flagRO, string(v.Int()), t)
  2433  }
  2434  
  2435  // convertOp: uintXX -> string
  2436  func cvtUintString(v Value, t Type) Value {
  2437  	return makeString(v.flag&flagRO, string(v.Uint()), t)
  2438  }
  2439  
  2440  // convertOp: []byte -> string
  2441  func cvtBytesString(v Value, t Type) Value {
  2442  	return makeString(v.flag&flagRO, string(v.Bytes()), t)
  2443  }
  2444  
  2445  // convertOp: string -> []byte
  2446  func cvtStringBytes(v Value, t Type) Value {
  2447  	return makeBytes(v.flag&flagRO, []byte(v.String()), t)
  2448  }
  2449  
  2450  // convertOp: []rune -> string
  2451  func cvtRunesString(v Value, t Type) Value {
  2452  	return makeString(v.flag&flagRO, string(v.runes()), t)
  2453  }
  2454  
  2455  // convertOp: string -> []rune
  2456  func cvtStringRunes(v Value, t Type) Value {
  2457  	return makeRunes(v.flag&flagRO, []rune(v.String()), t)
  2458  }
  2459  
  2460  // convertOp: direct copy
  2461  func cvtDirect(v Value, typ Type) Value {
  2462  	f := v.flag
  2463  	t := typ.common()
  2464  	val := v.val
  2465  	if f&flagAddr != 0 {
  2466  		// indirect, mutable word - make a copy
  2467  		ptr := unsafe_New(t)
  2468  		memmove(ptr, val, t.size)
  2469  		val = ptr
  2470  		f &^= flagAddr
  2471  	}
  2472  	return Value{t, val, v.flag&flagRO | f}
  2473  }
  2474  
  2475  // convertOp: concrete -> interface
  2476  func cvtT2I(v Value, typ Type) Value {
  2477  	target := new(interface{})
  2478  	x := valueInterface(v, false)
  2479  	if typ.NumMethod() == 0 {
  2480  		*target = x
  2481  	} else {
  2482  		ifaceE2I(typ.(*rtype), x, unsafe.Pointer(target))
  2483  	}
  2484  	return Value{typ.common(), unsafe.Pointer(target), v.flag&flagRO | flagIndir | flag(Interface)<<flagKindShift}
  2485  }
  2486  
  2487  // convertOp: interface -> interface
  2488  func cvtI2I(v Value, typ Type) Value {
  2489  	if v.IsNil() {
  2490  		ret := Zero(typ)
  2491  		ret.flag |= v.flag & flagRO
  2492  		return ret
  2493  	}
  2494  	return cvtT2I(v.Elem(), typ)
  2495  }
  2496  
  2497  // implemented in ../pkg/runtime
  2498  func chancap(ch iword) int
  2499  func chanclose(ch iword)
  2500  func chanlen(ch iword) int
  2501  func chanrecv(t *rtype, ch iword, nb bool) (val iword, selected, received bool)
  2502  func chansend(t *rtype, ch iword, val iword, nb bool) bool
  2503  
  2504  func makechan(typ *rtype, size uint64) (ch iword)
  2505  func makemap(t *rtype) (m iword)
  2506  func mapaccess(t *rtype, m iword, key iword) (val iword, ok bool)
  2507  func mapassign(t *rtype, m iword, key, val iword, ok bool)
  2508  func mapiterinit(t *rtype, m iword) *byte
  2509  func mapiterkey(it *byte) (key iword, ok bool)
  2510  func mapiternext(it *byte)
  2511  func maplen(m iword) int
  2512  
  2513  func call(fn, arg unsafe.Pointer, n uint32)
  2514  func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)
  2515  
  2516  // Dummy annotation marking that the value x escapes,
  2517  // for use in cases where the reflect code is so clever that
  2518  // the compiler cannot follow.
  2519  func escapes(x interface{}) {
  2520  	if dummy.b {
  2521  		dummy.x = x
  2522  	}
  2523  }
  2524  
  2525  var dummy struct {
  2526  	b bool
  2527  	x interface{}
  2528  }