作为接口传递时的 nil 切片不是 nil！为什么?(golang) [英] nil slice when passed as interface is not nil! Why? (golang)

问题描述

看到这个游乐场:http://play.golang.org/p/nWHmlw1W01

package main

import "fmt"

func main() {
    var i []int = nil
    yes(i) // output: true
    no(i)  // output: false
}

func yes(thing []int) {
    fmt.Println(thing == nil)
}

func no(thing interface{}) {
    fmt.Println(thing == nil)
}

为什么两个函数的输出不同?

Why the difference in output between the two functions?

推荐答案

诚然，这有点怪癖，但有一个解释.

Admittedly, it's somewhat of a quirk, but there's an explanation for it.

将 interface{} 变量想象成一个由两个字段组成的结构:一个是类型，另一个是数据.([]int 和 nil).实际上，它在 Go 运行时中看起来就是这样.

Imagine an interface{} variable as a struct composed of two fields: one is the type and another is the data. ([]int and nil). Actually, it looks just like that in the Go runtime.

struct Iface                                                                                                                   
{                                                                                                                              
    Itab*   tab;                                                                                                               
    void*   data;                                                                                                              
};   

当您将 nil 切片传递给 yes 时，只有 nil 作为值传递，因此您的比较归结为 nil == nil.

When you pass your nil slice to yes, only nil is passed as the value, so your comparison boils down to nil == nil.

同时，调用 no 会自动将您的变量包装在 interface{} 类型中，并且调用变得类似于 no(interface{[]int, nil}).所以no中的比较可以看成interface{[]int, nil} == nil，在go中结果为false.

Meanwhile, calling no automatically wraps your variable in an interface{} type and the call becomes something akin to no(interface{[]int, nil}). So the comparison in no could be seen as interface{[]int, nil} == nil, which turns out to be false in go.

该问题实际上已在 Go 常见问题解答中进行了解释.

The issue is actually explained in the Go FAQ.

这篇关于作为接口传递时的 nil 切片不是 nil！为什么?(golang)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！