Golang传递nil作为函数的可选参数? [英] Golang pass nil as optional argument to a function?

问题描述

在Golang中， http.NewRequest 具有如下规范:

In Golang, http.NewRequest has a specification like this:

func NewRequest(method, urlStr string, body io.Reader) (*Request, error)

但是，如果我不想将 body 传递给 io，则可以将 nil 作为 body 选项传递.Reader 对象，如下所示:

However, I can pass nil as the body option if I don't want to pass the body to an io.Reader object, like this:

req, err := http.NewRequest("GET", "http://www.blahblah.org", nil)

如何在代码中实现此功能?我有一个函数，我希望传递一个可选的字符串值，以便它可以分页显示API结果，但是如果我将 nil 传递给字符串输入，则会得到以下信息:

How do I implement this functionality in my code? I have a function that I want to pass an optional string value so that it can page through API results however if I pass a nil to the string input I get this:

./snippets.go:32:无法将nil转换为字符串类型

./snippets.go:32: cannot convert nil to type string

我的函数的参数如下:

func getChallenges(after string) ([]challenge, string, error)

推荐答案

Go没有可选"参数作为其他语言中普遍理解的概念； nil 只是接口的零值(在本例中为 io.Reader ).

Go does not have "optional" arguments as a generally understood concept in other languages; nil is just the zero value for an interface (io.Reader in this case).

字符串的等效零值是一个空字符串:

The equivalent zero value for a string is an empty string:

getChallenges("")

如果要接受0个或多个相同的参数类型，请使用可变参数语法:

If you want to accept 0 or more of the same argument type, you use the variadic syntax:

func getChallenges(after ...string) ([]challenge, string, error)

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