2018-03-23 11:06
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type SipField interface {
    Info() (id, name, defaultValue string, length int)

type Field string

func (f *Field) Get() string {
    return string(*f)

func (f *Field) Set(s string) {
    *f = Field(s)

type CommandID Field

func (cid *CommandID) Info() (id, name, defaultValue string, length int) {
    return "", "command ID", "", 2

type Language Field

func (l *Language) Info() (id, name, defaultValue string, length int) 
    return "", "language", "019", 3

func InitField(f interface{}, val string) error {
    sipField, ok := f.(SipField)
    if !ok {
        return errors.New("InitField: require a SipField")
    _, _, defaultValue, length := sipField.Info()
    field, ok := f.(*Field)
    if !ok {
     return errors.New("InitField: require a *Field")
    return nil

How should I do for converting interface{} to Field(CommandID, Language...) in InitField() function? I try to directly type assert by

field, ok := f.(*Field)

but it not working.I have tried to use unsafe.Pointer but failed also.

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  type SipField接口{
 Info()(ID,名称,defaultValue字符串,长度int)\  n} 
func(f * Field)Get()字符串{
返回字符串(* f)
func(f * Field)Set(s string){
  * f =字段
type CommandID字段
func(cid * CommandID)Info()(标识,名称,defaultValue字符串,长度int){
返回“”,“命令ID”  ,“”,2 
func(l * Language)Info()(id,名称,defaultValue字符串,长度int)
返回“”,“ language”,  “ 019”,3 
func InitField(f interface {},val string)error {
 sipField,ok:= f。(SipField)
 if!ok {
返回错误。New(“  InitField:需要一个SipField“)
 _,_,defaultValue,长度:= sipField.Info()
字段,确定:= f。(* Field)
,如果!ok {
返回错误。  New(“ InitField:require * Field”)

如何转换 interface {} Field(Com indField()函数中的mandID,语言...)? 我尝试直接通过

  field键入assert,好:= f。(* Field)

但是 它不起作用。我尝试使用unsafe.Pointer但也失败了。

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1条回答 默认 最新

  • douhan8430 2018-03-23 11:35

    Have a look at Type assertions chapter in Go reference. It states:


    More precisely, if T is not an interface type, x.(T) asserts that the dynamic type of x is identical to the type T.

    Types CommandID and Field are not identical as described in Type identity.

    A defined type is always different from any other type.

    Both types CommandId and Fields are defined as descirbed in Type definitions.

    A type definition creates a new, distinct type with the same underlying type and operations as the given type, and binds an identifier to it.

    TypeDef = identifier Type .

    You can only do

    field, ok := f.(*CommandID)


    field, ok := f.(*Language)

    As @mkopriva mentioned in the comment, you can do type conversion later to *Field but this it does not seem to be your goal.

    Other solution is to introduce a Field interface with Set and Get methods. Then you will need to provide an implementation for every implementing type.

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