go反射

Type Interface。Type 公有接口，rtype 结构是 Type 的一个实现。

基本类型结构体，静态类型信息，作为动态类型结构体的前半部分。动态类型信息的后半部分为，uncommonType。

// rtype is the common implementation of most values.
// It is embedded in other struct types.
//
// rtype must be kept in sync with ../runtime/type.go:/^type._type.
// 大部分对象的公共类型头信息 8个32位
type rtype struct {
	size       uintptr
	ptrdata    uintptr  // number of bytes in the type that can contain pointers
	hash       uint32   // hash of type; avoids computation in hash tables
	tflag      tflag    // extra type information flags
	align      uint8    // alignment of variable with this type
	fieldAlign uint8    // alignment of struct field with this type
	kind       uint8    // enumeration for C
	alg        *typeAlg // algorithm table
	gcdata     *byte    // garbage collection data
	str        nameOff  // string form
	ptrToThis  typeOff  // type for pointer to this type, may be zero
}

// uncommonType is present only for defined types or types with methods
// (if T is a defined type, the uncommonTypes for T and *T have methods).
// Using a pointer to this struct reduces the overall size required
// to describe a non-defined type with no methods.
// 记录包含方法的自定义类型的方法信息 reflect/type.go
type uncommonType struct {
	pkgPath nameOff // import path; empty for built-in types like int, string
	mcount  uint16  // number of methods
	xcount  uint16  // number of exported methods
	moff    uint32  // offset from this uncommontype to [mcount]method
	_       uint32  // unused
}

// Method on non-interface type
// 方法元数据,4个32位 offset 值
type method struct {
	name nameOff // name of method
	mtyp typeOff // method type (without receiver)
	ifn  textOff // fn used in interface call (one-word receiver)
	tfn  textOff // fn used for normal method call
}

// reflect/type.go
// 根据 uncommonTye 提取所有方法/所有导出方法
func (t *uncommonType) methods() []method {
	if t.mcount == 0 {
		return nil
	}
	return (*[1 << 16]method)(add(unsafe.Pointer(t), uintptr(t.moff), "t.mcount > 0"))[:t.mcount:t.mcount]
}

func (t *uncommonType) exportedMethods() []method {
	if t.xcount == 0 {
		return nil
	}
	return (*[1 << 16]method)(add(unsafe.Pointer(t), uintptr(t.moff), "t.xcount > 0"))[:t.xcount:t.xcount]
}

// reflect/type.go runtime/type.go
// 提取动态类型信息中的 uncommon 部分
func (t *_type) uncommon() *uncommontype {
	if t.tflag&tflagUncommon == 0 {
		return nil
	}
	switch t.kind & kindMask {
	case kindStruct:
		type u struct {
			structtype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindPtr:
		type u struct {
			ptrtype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindFunc:
		type u struct {
			functype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindSlice:
		type u struct {
			slicetype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindArray:
		type u struct {
			arraytype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindChan:
		type u struct {
			chantype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindMap:
		type u struct {
			maptype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindInterface:
		type u struct {
			interfacetype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	default:
		type u struct {
			_type
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	}
}

 

Interface

interface{} 对象头为一个指向静态类型信息的指针，TypeOf 直接提取该指针指向的类型信息。

// reflect/value.go
// emptyInterface is the header for an interface{} value.
type emptyInterface struct {
	typ  *rtype
	word unsafe.Pointer
}

// nonEmptyInterface is the header for an interface value with methods.
type nonEmptyInterface struct {
	// see ../runtime/iface.go:/Itab
	itab *struct {
		ityp *rtype // static interface type
		typ  *rtype // dynamic concrete type
		hash uint32 // copy of typ.hash
		_    [4]byte
		fun  [100000]unsafe.Pointer // method table
	}
	word unsafe.Pointer
}

// reflect/type.go
// TypeOf returns the reflection Type that represents the dynamic type of i.
// If i is a nil interface value, TypeOf returns nil.
func TypeOf(i interface{}) Type {
	eface := *(*emptyInterface)(unsafe.Pointer(&i))
	return toType(eface.typ)
}

 

Method() 方法

如果是 interface 直接根据 interface 结构体找到 methods，是 imethod 结构数组

如果不是则直接通过 uncommonType 找到 methods，是 method 结构数组，并调用 FuncOf

// reflect/type.go
// interfaceType represents an interface type.
// interface 的结构信息
type interfaceType struct {
	rtype
	pkgPath name      // import path
	methods []imethod // sorted by hash
}

// Method represents a single method.
type Method struct {
	// Name is the method name.
	// PkgPath is the package path that qualifies a lower case (unexported)
	// method name. It is empty for upper case (exported) method names.
	// The combination of PkgPath and Name uniquely identifies a method
	// in a method set.
	// See https://golang.org/ref/spec#Uniqueness_of_identifiers
	Name    string
	PkgPath string

	Type  Type  // method type
	Func  Value // func with receiver as first argument
	Index int   // index for Type.Method
}

// reflect.go
// 根据静态类型信息提取第 i 个方法
func (t *rtype) Method(i int) (m Method) {
	if t.Kind() == Interface {
		tt := (*interfaceType)(unsafe.Pointer(t))
		return tt.Method(i)
	}
	methods := t.exportedMethods()
	if i < 0 || i >= len(methods) {
		panic("reflect: Method index out of range")
	}
	p := methods[i]
	pname := t.nameOff(p.name)
	m.Name = pname.name()
	fl := flag(Func)
	mtyp := t.typeOff(p.mtyp)
	ft := (*funcType)(unsafe.Pointer(mtyp))
	in := make([]Type, 0, 1+len(ft.in()))
	in = append(in, t)
	for _, arg := range ft.in() {
		in = append(in, arg)
	}
	out := make([]Type, 0, len(ft.out()))
	for _, ret := range ft.out() {
		out = append(out, ret)
	}
	mt := FuncOf(in, out, ft.IsVariadic())
	m.Type = mt
	tfn := t.textOff(p.tfn)
	fn := unsafe.Pointer(&tfn)
	m.Func = Value{mt.(*rtype), fn, fl}

	m.Index = i
	return m
}

 

Type 中的其他方法类似，均是基于 rtype 通过指针运算返回相应类型信息。

 

 

Call