文章目录

• GoLang之图解反射
• • 1.前言
  • 2.Type
  • 3.Value

GoLang之图解反射

注：本文基于Windos系统上Go SDK v1.18进行讲解

1.前言

2.Type

//reflect/type.go
type Type interface {
    //以下是所有kind通用的方法
	Align() int //对齐边界
    FieldAlign() int //作为结构体字段的对齐边界
    Method(int) Method //获取方法数组中第i个Method
    MethodByName(string) (Method, bool) //按照名称查找方法
    NumMethod() int //方法列表中可导出方法的数目
    Name() string //类型名称
    PkgPath() string //包路径
    Size() uintptr //该类型变量占用字节数
    String() string //获取类型的字符串表示
    Kind() Kind //类型对应的reflect.Kind
    Implements(u Type) bool //该类型是否实现了接口u
    AssignableTo(u Type) bool //是否可以赋值给类型u
    ConvertibleTo(u Type) bool //是否可转换为类型u
    Comparable() bool //是否可比较

	//以下是某些Kind的方法
	//Int*, Uint*, Float*, Complex*: 
	Bits() int
    //Array,Ptr,Slice,Map: 
    Elem() Type
    //Array
    Len() int
    //Chan:ChanDir, Elem 
    ChanDir() ChanDir
    //Func: 
    In(i int) Type
    NumIn() int
    Out(i int) Type
    NumOut() int
    IsVariadic() bool
    //Map: 
    Key() Type
	//Struct: 
    Field(i int) StructField
    FieldByIndex(index []int) StructField
    FieldByName(name string) (StructField, bool)
    FieldByNameFunc(match func(string) bool) (StructField, bool)  
    NumField() int
	
	common() *rtype
	uncommon() *uncommonType
}

//reflect/type.go
func TypeOf(i any) Type {
	eface := *(*emptyInterface)(unsafe.Pointer(&i))
	return toType(eface.typ)
}

//builtin/builtin.go
type any = interface{}

a := "eggo"
t := reflect.TypeOf(a)

var ret reflect.Type
ret = eface.typ

//fmt/print.go
type Stringer interface {
    String() string
}

    var i interface{}
	a := 1
	i = a
	fmt.Println(a) //1
	fmt.Println(i) //1
	i = 5
	fmt.Println(a) //1
	fmt.Println(i) //5

    var i interface{}
	a := 1
	i = a
	fmt.Println(a) //1
	fmt.Println(i) //1
	a = 9
	fmt.Println(a) //9
	fmt.Println(i) //1

    var ii interface{}
	aa := []int{1, 2, 3}
	ii = aa
	fmt.Println(ii) //[1 2 3]
	fmt.Println(aa) //[1 2 3]
	aa[1] = 5
	fmt.Println(ii) //[1 5 3]
	fmt.Println(aa) //[1 5 3]

3.Value

//reflect/value.go
type Value struct {
    typ *rtype
    ptr unsafe.Pointer
    flag
}

//reflect/type.go
 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
	// function for comparing objects of this type
	// (ptr to object A, ptr to object B) -> ==?
	equal     func(unsafe.Pointer, unsafe.Pointer) bool
	gcdata    *byte   // garbage collection data
	str       nameOff // string form
	ptrToThis typeOff // type for pointer to this type, may be zero
}

func main() {
	a := "eggo"
	v := reflect.ValueOf(a)
	v.SetString("new eggo") //panic: reflect: reflect.Value.SetString using unaddressable value     运行错误
	println(a)
}

//reflect/value.go
func ValueOf(i any) Value {
    if i == nil {
        return Value{}
    }

    escapes(i)
    return unpackEface(i)
}

panic: reflect: reflect.Value.SetString using unaddressable value

func main() {
	a := "eggo"
	v := reflect.ValueOf(&a)
	v.Elem().SetString("new eggo")
	println(a) //new eggo
}