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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package reflect implements run-time reflection, allowing a program to
// manipulate objects with arbitrary types. The typical use is to take a value
// with static type interface{} and extract its dynamic type information by
// calling TypeOf, which returns a Type.
//
// A call to ValueOf returns a Value representing the run-time data.
// Zero takes a Type and returns a Value representing a zero value
// for that type.
//
// See "The Laws of Reflection" for an introduction to reflection in Go:
// http://blog.golang.org/2011/09/laws-of-reflection.html
package reflect
import (
"runtime"
"strconv"
"sync"
"unsafe"
)
// Type is the representation of a Go type.
//
// Not all methods apply to all kinds of types. Restrictions,
// if any, are noted in the documentation for each method.
// Use the Kind method to find out the kind of type before
// calling kind-specific methods. Calling a method
// inappropriate to the kind of type causes a run-time panic.
type Type interface {
// Methods applicable to all types.
// Align returns the alignment in bytes of a value of
// this type when allocated in memory.
Align() int
// FieldAlign returns the alignment in bytes of a value of
// this type when used as a field in a struct.
FieldAlign() int
// Method returns the i'th method in the type's method set.
// It panics if i is not in the range [0, NumMethod()).
//
// For a non-interface type T or *T, the returned Method's Type and Func
// fields describe a function whose first argument is the receiver.
//
// For an interface type, the returned Method's Type field gives the
// method signature, without a receiver, and the Func field is nil.
Method(int) Method
// MethodByName returns the method with that name in the type's
// method set and a boolean indicating if the method was found.
//
// For a non-interface type T or *T, the returned Method's Type and Func
// fields describe a function whose first argument is the receiver.
//
// For an interface type, the returned Method's Type field gives the
// method signature, without a receiver, and the Func field is nil.
MethodByName(string) (Method, bool)
// NumMethod returns the number of methods in the type's method set.
NumMethod() int
// Name returns the type's name within its package.
// It returns an empty string for unnamed types.
Name() string
// PkgPath returns the type's package path.
// The package path is a full package import path like "encoding/base64".
// PkgPath returns an empty string for unnamed or predeclared types.
PkgPath() string
// Size returns the number of bytes needed to store
// a value of the given type; it is analogous to unsafe.Sizeof.
Size() uintptr
// String returns a string representation of the type.
// The string representation may use shortened package names
// (e.g., base64 instead of "encoding/base64") and is not
// guaranteed to be unique among types. To test for equality,
// compare the Types directly.
String() string
// Kind returns the specific kind of this type.
Kind() Kind
// Implements returns true if the type implements the interface type u.
Implements(u Type) bool
// AssignableTo returns true if a value of the type is assignable to type u.
AssignableTo(u Type) bool
// Methods applicable only to some types, depending on Kind.
// The methods allowed for each kind are:
//
// Int*, Uint*, Float*, Complex*: Bits
// Array: Elem, Len
// Chan: ChanDir, Elem
// Func: In, NumIn, Out, NumOut, IsVariadic.
// Map: Key, Elem
// Ptr: Elem
// Slice: Elem
// Struct: Field, FieldByIndex, FieldByName, FieldByNameFunc, NumField
// Bits returns the size of the type in bits.
// It panics if the type's Kind is not one of the
// sized or unsized Int, Uint, Float, or Complex kinds.
Bits() int
// ChanDir returns a channel type's direction.
// It panics if the type's Kind is not Chan.
ChanDir() ChanDir
// IsVariadic returns true if a function type's final input parameter
// is a "..." parameter. If so, t.In(t.NumIn() - 1) returns the parameter's
// implicit actual type []T.
//
// For concreteness, if t represents func(x int, y ... float64), then
//
// t.NumIn() == 2
// t.In(0) is the reflect.Type for "int"
// t.In(1) is the reflect.Type for "[]float64"
// t.IsVariadic() == true
//
// IsVariadic panics if the type's Kind is not Func.
IsVariadic() bool
// Elem returns a type's element type.
// It panics if the type's Kind is not Array, Chan, Map, Ptr, or Slice.
Elem() Type
// Field returns a struct type's i'th field.
// It panics if the type's Kind is not Struct.
// It panics if i is not in the range [0, NumField()).
Field(i int) StructField
// FieldByIndex returns the nested field corresponding
// to the index sequence. It is equivalent to calling Field
// successively for each index i.
// It panics if the type's Kind is not Struct.
FieldByIndex(index []int) StructField
// FieldByName returns the struct field with the given name
// and a boolean indicating if the field was found.
FieldByName(name string) (StructField, bool)
// FieldByNameFunc returns the first struct field with a name
// that satisfies the match function and a boolean indicating if
// the field was found.
FieldByNameFunc(match func(string) bool) (StructField, bool)
// In returns the type of a function type's i'th input parameter.
// It panics if the type's Kind is not Func.
// It panics if i is not in the range [0, NumIn()).
In(i int) Type
// Key returns a map type's key type.
// It panics if the type's Kind is not Map.
Key() Type
// Len returns an array type's length.
// It panics if the type's Kind is not Array.
Len() int
// NumField returns a struct type's field count.
// It panics if the type's Kind is not Struct.
NumField() int
// NumIn returns a function type's input parameter count.
// It panics if the type's Kind is not Func.
NumIn() int
// NumOut returns a function type's output parameter count.
// It panics if the type's Kind is not Func.
NumOut() int
// Out returns the type of a function type's i'th output parameter.
// It panics if the type's Kind is not Func.
// It panics if i is not in the range [0, NumOut()).
Out(i int) Type
runtimeType() *runtime.Type
common() *commonType
uncommon() *uncommonType
}
// A Kind represents the specific kind of type that a Type represents.
// The zero Kind is not a valid kind.
type Kind uint
const (
Invalid Kind = iota
Bool
Int
Int8
Int16
Int32
Int64
Uint
Uint8
Uint16
Uint32
Uint64
Uintptr
Float32
Float64
Complex64
Complex128
Array
Chan
Func
Interface
Map
Ptr
Slice
String
Struct
UnsafePointer
)
/*
* Copy of data structures from ../runtime/type.go.
* For comments, see the ones in that file.
*
* These data structures are known to the compiler and the runtime.
*
* Putting these types in runtime instead of reflect means that
* reflect doesn't need to be autolinked into every binary, which
* simplifies bootstrapping and package dependencies.
* Unfortunately, it also means that reflect needs its own
* copy in order to access the private fields.
*/
// commonType is the common implementation of most values.
// It is embedded in other, public struct types, but always
// with a unique tag like `reflect:"array"` or `reflect:"ptr"`
// so that code cannot convert from, say, *arrayType to *ptrType.
type commonType struct {
size uintptr
hash uint32
_ uint8
align uint8
fieldAlign uint8
kind uint8
alg *uintptr
string *string
*uncommonType
ptrToThis *runtime.Type
}
type method struct {
name *string
pkgPath *string
mtyp *runtime.Type
typ *runtime.Type
ifn unsafe.Pointer
tfn unsafe.Pointer
}
type uncommonType struct {
name *string
pkgPath *string
methods []method
}
// ChanDir represents a channel type's direction.
type ChanDir int
const (
RecvDir ChanDir = 1 << iota
SendDir
BothDir = RecvDir | SendDir
)
// arrayType represents a fixed array type.
type arrayType struct {
commonType `reflect:"array"`
elem *runtime.Type
slice *runtime.Type
len uintptr
}
// chanType represents a channel type.
type chanType struct {
commonType `reflect:"chan"`
elem *runtime.Type
dir uintptr
}
// funcType represents a function type.
type funcType struct {
commonType `reflect:"func"`
dotdotdot bool
in []*runtime.Type
out []*runtime.Type
}
// imethod represents a method on an interface type
type imethod struct {
name *string
pkgPath *string
typ *runtime.Type
}
// interfaceType represents an interface type.
type interfaceType struct {
commonType `reflect:"interface"`
methods []imethod
}
// mapType represents a map type.
type mapType struct {
commonType `reflect:"map"`
key *runtime.Type
elem *runtime.Type
}
// ptrType represents a pointer type.
type ptrType struct {
commonType `reflect:"ptr"`
elem *runtime.Type
}
// sliceType represents a slice type.
type sliceType struct {
commonType `reflect:"slice"`
elem *runtime.Type
}
// Struct field
type structField struct {
name *string
pkgPath *string
typ *runtime.Type
tag *string
offset uintptr
}
// structType represents a struct type.
type structType struct {
commonType `reflect:"struct"`
fields []structField
}
/*
* The compiler knows the exact layout of all the data structures above.
* The compiler does not know about the data structures and methods below.
*/
// Method represents a single method.
type Method struct {
PkgPath string // empty for uppercase Name
Name string
Type Type
Func Value
Index int
}
// High bit says whether type has
// embedded pointers,to help garbage collector.
const kindMask = 0x7f
func (k Kind) String() string {
if int(k) < len(kindNames) {
return kindNames[k]
}
return "kind" + strconv.Itoa(int(k))
}
var kindNames = []string{
Invalid: "invalid",
Bool: "bool",
Int: "int",
Int8: "int8",
Int16: "int16",
Int32: "int32",
Int64: "int64",
Uint: "uint",
Uint8: "uint8",
Uint16: "uint16",
Uint32: "uint32",
Uint64: "uint64",
Uintptr: "uintptr",
Float32: "float32",
Float64: "float64",
Complex64: "complex64",
Complex128: "complex128",
Array: "array",
Chan: "chan",
Func: "func",
Interface: "interface",
Map: "map",
Ptr: "ptr",
Slice: "slice",
String: "string",
Struct: "struct",
UnsafePointer: "unsafe.Pointer",
}
func (t *uncommonType) uncommon() *uncommonType {
return t
}
func (t *uncommonType) PkgPath() string {
if t == nil || t.pkgPath == nil {
return ""
}
return *t.pkgPath
}
func (t *uncommonType) Name() string {
if t == nil || t.name == nil {
return ""
}
return *t.name
}
func (t *commonType) toType() Type {
if t == nil {
return nil
}
return t
}
func (t *commonType) String() string { return *t.string }
func (t *commonType) Size() uintptr { return t.size }
func (t *commonType) Bits() int {
if t == nil {
panic("reflect: Bits of nil Type")
}
k := t.Kind()
if k < Int || k > Complex128 {
panic("reflect: Bits of non-arithmetic Type " + t.String())
}
return int(t.size) * 8
}
func (t *commonType) Align() int { return int(t.align) }
func (t *commonType) FieldAlign() int { return int(t.fieldAlign) }
func (t *commonType) Kind() Kind { return Kind(t.kind & kindMask) }
func (t *commonType) common() *commonType { return t }
func (t *uncommonType) Method(i int) (m Method) {
if t == nil || i < 0 || i >= len(t.methods) {
panic("reflect: Method index out of range")
}
p := &t.methods[i]
if p.name != nil {
m.Name = *p.name
}
fl := flag(Func) << flagKindShift
if p.pkgPath != nil {
m.PkgPath = *p.pkgPath
fl |= flagRO
}
mt := toCommonType(p.typ)
m.Type = mt
fn := p.tfn
m.Func = Value{mt, fn, fl}
m.Index = i
return
}
func (t *uncommonType) NumMethod() int {
if t == nil {
return 0
}
return len(t.methods)
}
func (t *uncommonType) MethodByName(name string) (m Method, ok bool) {
if t == nil {
return
}
var p *method
for i := range t.methods {
p = &t.methods[i]
if p.name != nil && *p.name == name {
return t.Method(i), true
}
}
return
}
// TODO(rsc): 6g supplies these, but they are not
// as efficient as they could be: they have commonType
// as the receiver instead of *commonType.
func (t *commonType) NumMethod() int {
if t.Kind() == Interface {
tt := (*interfaceType)(unsafe.Pointer(t))
return tt.NumMethod()
}
return t.uncommonType.NumMethod()
}
func (t *commonType) Method(i int) (m Method) {
if t.Kind() == Interface {
tt := (*interfaceType)(unsafe.Pointer(t))
return tt.Method(i)
}
return t.uncommonType.Method(i)
}
func (t *commonType) MethodByName(name string) (m Method, ok bool) {
if t.Kind() == Interface {
tt := (*interfaceType)(unsafe.Pointer(t))
return tt.MethodByName(name)
}
return t.uncommonType.MethodByName(name)
}
func (t *commonType) PkgPath() string {
return t.uncommonType.PkgPath()
}
func (t *commonType) Name() string {
return t.uncommonType.Name()
}
func (t *commonType) ChanDir() ChanDir {
if t.Kind() != Chan {
panic("reflect: ChanDir of non-chan type")
}
tt := (*chanType)(unsafe.Pointer(t))
return ChanDir(tt.dir)
}
func (t *commonType) IsVariadic() bool {
if t.Kind() != Func {
panic("reflect: IsVariadic of non-func type")
}
tt := (*funcType)(unsafe.Pointer(t))
return tt.dotdotdot
}
func (t *commonType) Elem() Type {
switch t.Kind() {
case Array:
tt := (*arrayType)(unsafe.Pointer(t))
return toType(tt.elem)
case Chan:
tt := (*chanType)(unsafe.Pointer(t))
return toType(tt.elem)
case Map:
tt := (*mapType)(unsafe.Pointer(t))
return toType(tt.elem)
case Ptr:
tt := (*ptrType)(unsafe.Pointer(t))
return toType(tt.elem)
case Slice:
tt := (*sliceType)(unsafe.Pointer(t))
return toType(tt.elem)
}
panic("reflect; Elem of invalid type")
}
func (t *commonType) Field(i int) StructField {
if t.Kind() != Struct {
panic("reflect: Field of non-struct type")
}
tt := (*structType)(unsafe.Pointer(t))
return tt.Field(i)
}
func (t *commonType) FieldByIndex(index []int) StructField {
if t.Kind() != Struct {
panic("reflect: FieldByIndex of non-struct type")
}
tt := (*structType)(unsafe.Pointer(t))
return tt.FieldByIndex(index)
}
func (t *commonType) FieldByName(name string) (StructField, bool) {
if t.Kind() != Struct {
panic("reflect: FieldByName of non-struct type")
}
tt := (*structType)(unsafe.Pointer(t))
return tt.FieldByName(name)
}
func (t *commonType) FieldByNameFunc(match func(string) bool) (StructField, bool) {
if t.Kind() != Struct {
panic("reflect: FieldByNameFunc of non-struct type")
}
tt := (*structType)(unsafe.Pointer(t))
return tt.FieldByNameFunc(match)
}
func (t *commonType) In(i int) Type {
if t.Kind() != Func {
panic("reflect: In of non-func type")
}
tt := (*funcType)(unsafe.Pointer(t))
return toType(tt.in[i])
}
func (t *commonType) Key() Type {
if t.Kind() != Map {
panic("reflect: Key of non-map type")
}
tt := (*mapType)(unsafe.Pointer(t))
return toType(tt.key)
}
func (t *commonType) Len() int {
if t.Kind() != Array {
panic("reflect: Len of non-array type")
}
tt := (*arrayType)(unsafe.Pointer(t))
return int(tt.len)
}
func (t *commonType) NumField() int {
if t.Kind() != Struct {
panic("reflect: NumField of non-struct type")
}
tt := (*structType)(unsafe.Pointer(t))
return len(tt.fields)
}
func (t *commonType) NumIn() int {
if t.Kind() != Func {
panic("reflect; NumIn of non-func type")
}
tt := (*funcType)(unsafe.Pointer(t))
return len(tt.in)
}
func (t *commonType) NumOut() int {
if t.Kind() != Func {
panic("reflect; NumOut of non-func type")
}
tt := (*funcType)(unsafe.Pointer(t))
return len(tt.out)
}
func (t *commonType) Out(i int) Type {
if t.Kind() != Func {
panic("reflect: Out of non-func type")
}
tt := (*funcType)(unsafe.Pointer(t))
return toType(tt.out[i])
}
func (d ChanDir) String() string {
switch d {
case SendDir:
return "chan<-"
case RecvDir:
return "<-chan"
case BothDir:
return "chan"
}
return "ChanDir" + strconv.Itoa(int(d))
}
// Method returns the i'th method in the type's method set.
func (t *interfaceType) Method(i int) (m Method) {
if i < 0 || i >= len(t.methods) {
return
}
p := &t.methods[i]
m.Name = *p.name
if p.pkgPath != nil {
m.PkgPath = *p.pkgPath
}
m.Type = toType(p.typ)
m.Index = i
return
}
// NumMethod returns the number of interface methods in the type's method set.
func (t *interfaceType) NumMethod() int { return len(t.methods) }
// MethodByName method with the given name in the type's method set.
func (t *interfaceType) MethodByName(name string) (m Method, ok bool) {
if t == nil {
return
}
var p *imethod
for i := range t.methods {
p = &t.methods[i]
if *p.name == name {
return t.Method(i), true
}
}
return
}
type StructField struct {
PkgPath string // empty for uppercase Name
Name string
Type Type
Tag StructTag
Offset uintptr
Index []int
Anonymous bool
}
// A StructTag is the tag string in a struct field.
//
// By convention, tag strings are a concatenation of
// optionally space-separated key:"value" pairs.
// Each key is a non-empty string consisting of non-control
// characters other than space (U+0020 ' '), quote (U+0022 '"'),
// and colon (U+003A ':'). Each value is quoted using U+0022 '"'
// characters and Go string literal syntax.
type StructTag string
// Get returns the value associated with key in the tag string.
// If there is no such key in the tag, Get returns the empty string.
// If the tag does not have the conventional format, the value
// returned by Get is unspecified.
func (tag StructTag) Get(key string) string {
for tag != "" {
// skip leading space
i := 0
for i < len(tag) && tag[i] == ' ' {
i++
}
tag = tag[i:]
if tag == "" {
break
}
// scan to colon.
// a space or a quote is a syntax error
i = 0
for i < len(tag) && tag[i] != ' ' && tag[i] != ':' && tag[i] != '"' {
i++
}
if i+1 >= len(tag) || tag[i] != ':' || tag[i+1] != '"' {
break
}
name := string(tag[:i])
tag = tag[i+1:]
// scan quoted string to find value
i = 1
for i < len(tag) && tag[i] != '"' {
if tag[i] == '\\' {
i++
}
i++
}
if i >= len(tag) {
break
}
qvalue := string(tag[:i+1])
tag = tag[i+1:]
if key == name {
value, _ := strconv.Unquote(qvalue)
return value
}
}
return ""
}
// Field returns the i'th struct field.
func (t *structType) Field(i int) (f StructField) {
if i < 0 || i >= len(t.fields) {
return
}
p := &t.fields[i]
f.Type = toType(p.typ)
if p.name != nil {
f.Name = *p.name
} else {
t := f.Type
if t.Kind() == Ptr {
t = t.Elem()
}
f.Name = t.Name()
f.Anonymous = true
}
if p.pkgPath != nil {
f.PkgPath = *p.pkgPath
}
if p.tag != nil {
f.Tag = StructTag(*p.tag)
}
f.Offset = p.offset
// NOTE(rsc): This is the only allocation in the interface
// presented by a reflect.Type. It would be nice to avoid,
// at least in the common cases, but we need to make sure
// that misbehaving clients of reflect cannot affect other
// uses of reflect. One possibility is CL 5371098, but we
// postponed that ugliness until there is a demonstrated
// need for the performance. This is issue 2320.
f.Index = []int{i}
return
}
// TODO(gri): Should there be an error/bool indicator if the index
// is wrong for FieldByIndex?
// FieldByIndex returns the nested field corresponding to index.
func (t *structType) FieldByIndex(index []int) (f StructField) {
f.Type = Type(t.toType())
for i, x := range index {
if i > 0 {
ft := f.Type
if ft.Kind() == Ptr && ft.Elem().Kind() == Struct {
ft = ft.Elem()
}
f.Type = ft
}
f = f.Type.Field(x)
}
return
}
const inf = 1 << 30 // infinity - no struct has that many nesting levels
func (t *structType) fieldByNameFunc(match func(string) bool, mark map[*structType]bool, depth int) (ff StructField, fd int) {
fd = inf // field depth
if mark[t] {
// Struct already seen.
return
}
mark[t] = true
var fi int // field index
n := 0 // number of matching fields at depth fd
L:
for i := range t.fields {
f := t.Field(i)
d := inf
switch {
case match(f.Name):
// Matching top-level field.
d = depth
case f.Anonymous:
ft := f.Type
if ft.Kind() == Ptr {
ft = ft.Elem()
}
switch {
case match(ft.Name()):
// Matching anonymous top-level field.
d = depth
case fd > depth:
// No top-level field yet; look inside nested structs.
if ft.Kind() == Struct {
st := (*structType)(unsafe.Pointer(ft.(*commonType)))
f, d = st.fieldByNameFunc(match, mark, depth+1)
}
}
}
switch {
case d < fd:
// Found field at shallower depth.
ff, fi, fd = f, i, d
n = 1
case d == fd:
// More than one matching field at the same depth (or d, fd == inf).
// Same as no field found at this depth.
n++
if d == depth {
// Impossible to find a field at lower depth.
break L
}
}
}
if n == 1 {
// Found matching field.
if depth >= len(ff.Index) {
ff.Index = make([]int, depth+1)
}
if len(ff.Index) > 1 {
ff.Index[depth] = fi
}
} else {
// None or more than one matching field found.
fd = inf
}
delete(mark, t)
return
}
// FieldByName returns the struct field with the given name
// and a boolean to indicate if the field was found.
func (t *structType) FieldByName(name string) (f StructField, present bool) {
return t.FieldByNameFunc(func(s string) bool { return s == name })
}
// FieldByNameFunc returns the struct field with a name that satisfies the
// match function and a boolean to indicate if the field was found.
func (t *structType) FieldByNameFunc(match func(string) bool) (f StructField, present bool) {
if ff, fd := t.fieldByNameFunc(match, make(map[*structType]bool), 0); fd < inf {
ff.Index = ff.Index[0 : fd+1]
f, present = ff, true
}
return
}
// Convert runtime type to reflect type.
func toCommonType(p *runtime.Type) *commonType {
if p == nil {
return nil
}
type hdr struct {
x interface{}
t commonType
}
x := unsafe.Pointer(p)
return &(*hdr)(x).t
}
func toType(p *runtime.Type) Type {
if p == nil {
return nil
}
return toCommonType(p).toType()
}
// TypeOf returns the reflection Type of the value in the interface{}.
func TypeOf(i interface{}) Type {
eface := *(*emptyInterface)(unsafe.Pointer(&i))
return toType(eface.typ)
}
// ptrMap is the cache for PtrTo.
var ptrMap struct {
sync.RWMutex
m map[*commonType]*ptrType
}
func (t *commonType) runtimeType() *runtime.Type {
// The runtime.Type always precedes the commonType in memory.
// Adjust pointer to find it.
var rt struct {
i runtime.Type
ct commonType
}
return (*runtime.Type)(unsafe.Pointer(uintptr(unsafe.Pointer(t)) - unsafe.Offsetof(rt.ct)))
}
// PtrTo returns the pointer type with element t.
// For example, if t represents type Foo, PtrTo(t) represents *Foo.
func PtrTo(t Type) Type {
return t.(*commonType).ptrTo()
}
func (ct *commonType) ptrTo() *commonType {
if p := ct.ptrToThis; p != nil {
return toCommonType(p)
}
// Otherwise, synthesize one.
// This only happens for pointers with no methods.
// We keep the mapping in a map on the side, because
// this operation is rare and a separate map lets us keep
// the type structures in read-only memory.
ptrMap.RLock()
if m := ptrMap.m; m != nil {
if p := m[ct]; p != nil {
ptrMap.RUnlock()
return &p.commonType
}
}
ptrMap.RUnlock()
ptrMap.Lock()
if ptrMap.m == nil {
ptrMap.m = make(map[*commonType]*ptrType)
}
p := ptrMap.m[ct]
if p != nil {
// some other goroutine won the race and created it
ptrMap.Unlock()
return &p.commonType
}
var rt struct {
i runtime.Type
ptrType
}
rt.i = (*runtime.PtrType)(unsafe.Pointer(&rt.ptrType))
// initialize p using *byte's ptrType as a prototype.
// have to do assignment as ptrType, not runtime.PtrType,
// in order to write to unexported fields.
p = &rt.ptrType
bp := (*ptrType)(unsafe.Pointer(unsafe.Typeof((*byte)(nil)).(*runtime.PtrType)))
*p = *bp
s := "*" + *ct.string
p.string = &s
// For the type structures linked into the binary, the
// compiler provides a good hash of the string.
// Create a good hash for the new string by using
// the FNV-1 hash's mixing function to combine the
// old hash and the new "*".
p.hash = ct.hash*16777619 ^ '*'
p.uncommonType = nil
p.ptrToThis = nil
p.elem = (*runtime.Type)(unsafe.Pointer(uintptr(unsafe.Pointer(ct)) - unsafe.Offsetof(rt.ptrType)))
ptrMap.m[ct] = p
ptrMap.Unlock()
return &p.commonType
}
func (t *commonType) Implements(u Type) bool {
if u == nil {
panic("reflect: nil type passed to Type.Implements")
}
if u.Kind() != Interface {
panic("reflect: non-interface type passed to Type.Implements")
}
return implements(u.(*commonType), t)
}
func (t *commonType) AssignableTo(u Type) bool {
if u == nil {
panic("reflect: nil type passed to Type.AssignableTo")
}
uu := u.(*commonType)
return directlyAssignable(uu, t) || implements(uu, t)
}
// implements returns true if the type V implements the interface type T.
func implements(T, V *commonType) bool {
if T.Kind() != Interface {
return false
}
t := (*interfaceType)(unsafe.Pointer(T))
if len(t.methods) == 0 {
return true
}
// The same algorithm applies in both cases, but the
// method tables for an interface type and a concrete type
// are different, so the code is duplicated.
// In both cases the algorithm is a linear scan over the two
// lists - T's methods and V's methods - simultaneously.
// Since method tables are stored in a unique sorted order
// (alphabetical, with no duplicate method names), the scan
// through V's methods must hit a match for each of T's
// methods along the way, or else V does not implement T.
// This lets us run the scan in overall linear time instead of
// the quadratic time a naive search would require.
// See also ../runtime/iface.c.
if V.Kind() == Interface {
v := (*interfaceType)(unsafe.Pointer(V))
i := 0
for j := 0; j < len(v.methods); j++ {
tm := &t.methods[i]
vm := &v.methods[j]
if vm.name == tm.name && vm.pkgPath == tm.pkgPath && vm.typ == tm.typ {
if i++; i >= len(t.methods) {
return true
}
}
}
return false
}
v := V.uncommon()
if v == nil {
return false
}
i := 0
for j := 0; j < len(v.methods); j++ {
tm := &t.methods[i]
vm := &v.methods[j]
if vm.name == tm.name && vm.pkgPath == tm.pkgPath && vm.mtyp == tm.typ {
if i++; i >= len(t.methods) {
return true
}
}
}
return false
}
// directlyAssignable returns true if a value x of type V can be directly
// assigned (using memmove) to a value of type T.
// http://golang.org/doc/go_spec.html#Assignability
// Ignoring the interface rules (implemented elsewhere)
// and the ideal constant rules (no ideal constants at run time).
func directlyAssignable(T, V *commonType) bool {
// x's type V is identical to T?
if T == V {
return true
}
// Otherwise at least one of T and V must be unnamed
// and they must have the same kind.
if T.Name() != "" && V.Name() != "" || T.Kind() != V.Kind() {
return false
}
// x's type T and V have identical underlying types.
// Since at least one is unnamed, only the composite types
// need to be considered.
switch T.Kind() {
case Array:
return T.Elem() == V.Elem() && T.Len() == V.Len()
case Chan:
// Special case:
// x is a bidirectional channel value, T is a channel type,
// and x's type V and T have identical element types.
if V.ChanDir() == BothDir && T.Elem() == V.Elem() {
return true
}
// Otherwise continue test for identical underlying type.
return V.ChanDir() == T.ChanDir() && T.Elem() == V.Elem()
case Func:
t := (*funcType)(unsafe.Pointer(T))
v := (*funcType)(unsafe.Pointer(V))
if t.dotdotdot != v.dotdotdot || len(t.in) != len(v.in) || len(t.out) != len(v.out) {
return false
}
for i, typ := range t.in {
if typ != v.in[i] {
return false
}
}
for i, typ := range t.out {
if typ != v.out[i] {
return false
}
}
return true
case Interface:
t := (*interfaceType)(unsafe.Pointer(T))
v := (*interfaceType)(unsafe.Pointer(V))
if len(t.methods) == 0 && len(v.methods) == 0 {
return true
}
// Might have the same methods but still
// need a run time conversion.
return false
case Map:
return T.Key() == V.Key() && T.Elem() == V.Elem()
case Ptr, Slice:
return T.Elem() == V.Elem()
case Struct:
t := (*structType)(unsafe.Pointer(T))
v := (*structType)(unsafe.Pointer(V))
if len(t.fields) != len(v.fields) {
return false
}
for i := range t.fields {
tf := &t.fields[i]
vf := &v.fields[i]
if tf.name != vf.name || tf.pkgPath != vf.pkgPath ||
tf.typ != vf.typ || tf.tag != vf.tag || tf.offset != vf.offset {
return false
}
}
return true
}
return false
}