如果结构具有参数实现接口的功能，则结构不实现接口 [英] Struct does not implement interface if it has a function which parameter implement interface

问题描述

我有一个包含两个接口的程序包

I have a package in which I have two interfaces

package main
type A interface {
    Close()
}
type B interface {
    Connect() (A, error)
}

我还有两个实现这些接口的结构

I have also two structures which implements these interfaces

type C struct {
}

func (c *C) Close() {

}

type D struct {
}

func (d *D) Connect() (*C, error) {
    c := new(C)
    return c, nil
}

接下来，我有一个函数，该函数需要一个实现接口B的对象作为参数

Next I have a function which as a parameter wants an object which implements interface B

func test(b B) {
}

最后，在main()函数中，我创建了D结构对象并想调用test()函数

Finally, at the main() function I create D structure object and want to call test() function

func main() {
    d := new(D)
    test(d)
}

如果我尝试构建该软件包，则会出错.

If I try to build that package I have an error.

不能在测试参数中使用d(* D型)作为B型: * D没有实现B(Connect方法的类型错误) 有Connect()(* C，错误) 想要Connect()(A，错误)

cannot use d (type *D) as type B in argument to test: *D does not implement B (wrong type for Connect method) have Connect() (*C, error) want Connect() (A, error)

这是我的代码的简单示例，其中我使用外部包并希望模拟结构进行测试.使用接口代替类型有什么解决方案吗?

It is simple example of my code where I use external package and want to mock structures for tests. Is it any solution to use interfaces instead of types?

推荐答案

Connect方法的返回类型应为A而不是*C.

The returned type for your Connect method should be A and not *C.

您定义Connect方法的方式是它应该返回接口，而不是特定类型.您仍然可以返回*C，因为它实现了A接口.

The way you defined the Connect method is that it should return an interface, not a specific type. You will still be able to return *C as it implements the A interface.

package main

type A interface {
    Close()
}

type B interface {
    Connect() (A, error)
}

type C struct {
}

func (c *C) Close() {
}

type D struct {
}

func (d *D) Connect() (A, error) {
    c := new(C)
    println("successfully created new C:", c)
    return c, nil
}

func test(b B) {
    b.Connect()
}

func main() {
    d := new(D)
    test(d)
}

输出

成功创建了新的C:0xe28f0

successfully created new C: 0xe28f0

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