Golang方法与指针接收器 [英] Golang method with pointer receiver

问题描述

我有这个示例代码

 包主
 
导入（
fmt 
）
 
类型IFace接口{
 SetSomeField（newValue字符串）
 GetSomeField（）字符串
} 
 
类型实现struct {
 someField string 
} 
 
 func（i Implementation）GetSomeField（）string {
 return i.someField 
} 
 
 func（i Implementation）SetSomeField（newValue string）{
 i.someField = newValue 
} 
 
 func Create（）IFace {
 obj：= Implementation { someField：Hello} 
 return obj //< =违规行
} 
 
 func main（）{
a：= Create（）
 a.SetSomeField（World）
 fmt.Println（a.GetSomeField（））
} 
  

$ p












$ p $我将该方法更改为指针接收器，我期望能够工作，它看起来像这样：

  func（i *实现）SetSomeField（newValue string）{... 
  

编译会导致以下错误：

  prog .go：26：在返回参数中不能使用obj（类型实现）作为IFace类型：
实现没有实现IFace（GetSomeField方法有指针接收器）
  

如何让 struct 实现接口和方法 SetSomeField 在不创建副本的情况下更改实际实例的值

这里有一个可破解的代码片段：
https://play.golang.org/p/ghW0mk0IuU

我已经看到这个问题在go（golang）中，如何将接口指针转换为结构指针？，但我不明白它与这个例子有什么关系。

解决方案

结构的指针应该实现接口。以这种方式，你可以修改它的字段。

看看我如何修改你的代码，使它按照你的预期工作：

 包主要
 
导入（
fmt
）
 
 IFace界面{ 
 SetSomeField（newValue字符串）
 GetSomeField（）字符串
} 
 
类型实现struct {
 someField字符串
} 
 
 func（i *实现）GetSomeField（）字符串{
返回i.someField 
} 
 
 func（i *实现）SetSomeField（newValue string）{
 i.someField = newValue 
} 
 
 func Create（）* Implementation {
 return& Implementation {someField：Hello} 
} 
 
 func main（）{
 var a IFace 
a = Create（）
 a.SetSomeField（World）
 fmt.Println（a.GetSomeField（）） 
} 
  

I have this example code

package main

import (
    "fmt"
)

type IFace interface {
    SetSomeField(newValue string)
    GetSomeField() string
}

type Implementation struct {
    someField string
}

func (i Implementation) GetSomeField() string {
    return i.someField
}

func (i Implementation) SetSomeField(newValue string) {
    i.someField = newValue
}

func Create() IFace {
    obj := Implementation{someField: "Hello"}
    return obj // <= Offending line
}

func main() {
    a := Create()
    a.SetSomeField("World")
    fmt.Println(a.GetSomeField())
}

SetSomeField does not work as expected because its receiver is not of pointer type.

If I change the method to a pointer receiver, what I would expect to work, it looks like this:

func (i *Implementation) SetSomeField(newValue string) { ...

Compiling this leads to the following error:

prog.go:26: cannot use obj (type Implementation) as type IFace in return argument:
Implementation does not implement IFace (GetSomeField method has pointer receiver)

How can I have the struct implement the interface and the method SetSomeField change the value of the actual instance without creating a copy?

Here's a hackable snippet: https://play.golang.org/p/ghW0mk0IuU

I've already seen this question In go (golang), how can you cast an interface pointer into a struct pointer?, but I cannot see how it is related to this example.

解决方案

Your pointer to the struct should implement the Interface. In that way you can modify its fields.

Look at how I modified your code, to make it working as you expect:

package main

import (
    "fmt"
)

type IFace interface {
    SetSomeField(newValue string)
    GetSomeField() string
}

type Implementation struct {
    someField string
}    

func (i *Implementation) GetSomeField() string {
    return i.someField
}

func (i *Implementation) SetSomeField(newValue string) {
    i.someField = newValue
}

func Create() *Implementation {
    return &Implementation{someField: "Hello"}
}

func main() {
    var a IFace
    a = Create()
    a.SetSomeField("World")
    fmt.Println(a.GetSomeField())
}

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