“方法需要指示器接收器”在Go编程语言中 [英] "method requires pointer receiver" in Go Programming Language

问题描述

我刚刚看到Go编程语言的演示文稿，并认为我会尝试写几行。一切工作正常，直到我试图在这种情况下使用接口。如何解决这个问题？

I just saw a presentation of the Go programming language and thought I'd try to write a few lines. Everything worked fine until I tried to use an interface in this situation. How do I solve this?

package main

import "fmt"

type entity float32

func (e *entity) inc() {
    *e++
}

type incer interface {
    inc()
}

func doSomething(i incer) {
    i.inc()
}

func main() {
    fmt.Println("Hello, 世界")

    var e entity = 3
    e.inc()
    doSomething(e)
    fmt.Println(e)
}

我得到编译器错误：

prog.go:24: cannot use e (type entity) as type incer in function argument:
entity does not implement incer (inc method requires pointer receiver)

我想使用一个指针，以便inc（）会影响外部的enity功能。什么是我应该使用的语法？

I want to use a pointer so that the inc() will affect the enity outside the function. What is the syntax I should use?

/ Ricky

推荐答案

我认为这里有一些困惑。 inc 是类型 *实体类型的方法，而不是类型 entity code>（虽然你可以直接在指针上调用值的方法，但你通常不能直接在指针上调用方法）。您可能会困惑的是为什么您可以调用 e.inc（），而不必执行（& e）.inc（） 。这是一个鲜为人知的特例，记录在语言的通话部分底部说明如果 x 是可寻址的，并且& x 的方法集包含 m ，那么 xm（）是（& x）.m（）。这适用于这种情况，因为 e 是一个变量，所以它是可寻址的;但其他表达式可能不可寻址。但是，我建议您不要使用这个快捷方式，因为这会造成混淆;它让你认为 e 符合接口 inter ，而不是。

I think there is some confusion here. inc is a method of the type *entity, and not of the type entity (while you can call methods on values directly on pointers; you cannot generally call methods on pointers directly on values). What you may be confused about is why you could call e.inc(), instead of having to do (&e).inc(). This is a little-known special case documented at the bottom of the Calls section in the language specification, that says if x is addressable, and &x's method set contains m, then x.m() is shorthand for (&x).m(). This applies to this case because e is a variable, so it is addressable; but other expressions may not be addressable. I would recommend that you not use this shortcut, however, as it causes confusion; it makes you think that e conforms to the interface inter, while it does not.

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