输入错误:结构未实现接口 [英] Go type-error: struct does not implement interface

问题描述

// BEGIN: external library

type realX struct {}

type realY struct {}

func (realX) Do() realY {
  return realY{}
}

// END

type A struct {
  a myX
}

type myY interface {}

type myX interface {
  Do() myY
}

func foo (arg1 myY) {
}

func main() {
    foo(realY{})
    x := A{realX{}}
    fmt.Println("Hello, playground")
}

我得到:

cannot use realX literal (type realX) as type myX in field value:
    realX does not implement myX (wrong type for Do method)
        have Do() realY
        want Do() myY

从外观上看，realY实现了myY，为什么我不能这样做呢?这使得不可能干净地编写模拟单元测试.

From the looks of it, realY implements myY, so why can't I do this? This is making it impossible to write mock unit tests cleanly.

推荐答案

不，它没有实现myY，因为错误明确指出:

No, it doesn't implement myY, as the error clearly states:

realX does not implement myX (wrong type for Do method)
    have Do() realY
    want Do() myY

用于实现接口的类型的方法签名必须完全匹配.方法签名不匹配-返回类型不同. realY是否实现myY无关紧要；签名不一样.

The method signature must match exactly for the type to implement the interface. The method signatures do not match - the return types are different. It doesn't matter if realY implements myY; the signatures are not the same.

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