github.com/goplus/yap@v0.8.1/reflectutil/value.go (about)

     1  /*
     2   * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
     3   *
     4   * Licensed under the Apache License, Version 2.0 (the "License");
     5   * you may not use this file except in compliance with the License.
     6   * You may obtain a copy of the License at
     7   *
     8   *     http://www.apache.org/licenses/LICENSE-2.0
     9   *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  
    17  package reflectutil
    18  
    19  import (
    20  	"reflect"
    21  	"unsafe"
    22  )
    23  
    24  type flag uintptr
    25  
    26  const (
    27  	flagKindWidth        = 5 // there are 27 kinds
    28  	flagKindMask    flag = 1<<flagKindWidth - 1
    29  	flagStickyRO    flag = 1 << 5
    30  	flagEmbedRO     flag = 1 << 6
    31  	flagIndir       flag = 1 << 7
    32  	flagAddr        flag = 1 << 8
    33  	flagMethod      flag = 1 << 9
    34  	flagMethodShift      = 10
    35  	flagRO          flag = flagStickyRO | flagEmbedRO
    36  )
    37  
    38  type value struct {
    39  	// typ_ holds the type of the value represented by a Value.
    40  	// Access using the typ method to avoid escape of v.
    41  	typ_ unsafe.Pointer
    42  
    43  	// Pointer-valued data or, if flagIndir is set, pointer to data.
    44  	// Valid when either flagIndir is set or typ.pointers() is true.
    45  	ptr unsafe.Pointer
    46  
    47  	// flag holds metadata about the value.
    48  	//
    49  	// The lowest five bits give the Kind of the value, mirroring typ.Kind().
    50  	//
    51  	// The next set of bits are flag bits:
    52  	//	- flagStickyRO: obtained via unexported not embedded field, so read-only
    53  	//	- flagEmbedRO: obtained via unexported embedded field, so read-only
    54  	//	- flagIndir: val holds a pointer to the data
    55  	//	- flagAddr: v.CanAddr is true (implies flagIndir and ptr is non-nil)
    56  	//	- flagMethod: v is a method value.
    57  	// If ifaceIndir(typ), code can assume that flagIndir is set.
    58  	//
    59  	// The remaining 22+ bits give a method number for method values.
    60  	// If flag.kind() != Func, code can assume that flagMethod is unset.
    61  	flag
    62  
    63  	// A method value represents a curried method invocation
    64  	// like r.Read for some receiver r. The typ+val+flag bits describe
    65  	// the receiver r, but the flag's Kind bits say Func (methods are
    66  	// functions), and the top bits of the flag give the method number
    67  	// in r's type's method table.
    68  }
    69  
    70  func UnsafeAddr(v reflect.Value) uintptr {
    71  	(*value)(unsafe.Pointer(&v)).flag |= flagAddr
    72  	return v.UnsafeAddr()
    73  }