斯金格斯的困惑行为? [英] puzzling behavior for Stringers?

问题描述

Go的新手，所以请忍受我.

New to Go, so please bear with me.

我一直在浏览去旅行"页面，偶然发现一些关于斯金格斯的困惑.在 https://tour.golang.org/methods/18

I've been looking at the "Tour of Go" pages, and stumbled into something puzzling about Stringers. Consider the exercise at https://tour.golang.org/methods/18

我最初的答案是实施

func (this *IPAddr) String() string {
  return fmt.Sprintf("%d.%d.%d.%d", this[0], this[1], this[2], this[3])
}

但是，仅用于fmt.Printf("%v: %v\n", name, ip)的主要打印内容不使用此功能.如果我将打印内容更改为fmt.Printf("%v: %v\n", name, ip.String())，则无论接收器类型是*IPAddr还是IPAddr，都将使用它.

however, this is not used f main prints just fmt.Printf("%v: %v\n", name, ip). If I change the print to fmt.Printf("%v: %v\n", name, ip.String()), then it is used whether the receiver type is *IPAddr or IPAddr).

为什么会这样?

推荐答案

由于要向fmt.Printf传递IPAddr值，因此String()方法不属于方法集.如果传递指针，您的解决方案将起作用:

Because you're passing an IPAddr value to fmt.Printf, your String() method isn't part of the method set. Your solution works if you pass in a pointer:

fmt.Printf("%v: %v\n", name, &ip)

但是一般的解决方案是不使用指针接收器:

But a general solution is to not use a pointer receiver:

func (ip IPAddr) String() string {
  return fmt.Sprintf("%d.%d.%d.%d", ip[0], ip[1], ip[2], ip[3])
}

这样，可以从要传递给Printf的IPAddr或包括值接收器的方法的*IPAddr中使用String()方法.

This way the String() method can be used from an IPAddr, which is what you're passing to Printf, or an *IPAddr, which includes the methods of the value receiver.

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