为什么我不能在Go中使用new()初始化地图? [英] Why can't I initialize a map with new() in Go?

问题描述

package main

import "fmt"

func main() {
    p := new(map[string]int)
    m := make(map[string]int)
    m["in m"] = 2
    (*p)["in p"] = 1
    fmt.Println(m)
    fmt.Println(*p)
}

上面的代码给出了错误 panic:分配给nil map中的条目.如果在将成对插入之前打印 * p ，则输出正确.看来我无法修改 * p ?

The above code gives an error panic: assignment to entry in nil map. If I print *p before inserting pairs into it, the output is correct. It seems I just can't modify *p?

推荐答案

这不是与 new 关键字直接相关的问题.如果未初始化地图，则使用 var 关键字声明地图时，会得到相同的行为，例如:

This is not directly an issue with new keyword. You would get the same behavior, if you did not initialize your map, when declaring it with var keyword, for example:

var a map[string]int
a["z"] = 10

解决此问题的方法是初始化地图:

The way to fix this is to initialize the map:

var a map[string]int
a = map[string]int{}
a["z"] = 10

它与 new 关键字的工作方式相同:

And it works the same way, with new keyword:

p := new(map[string]int)
*p = map[string]int{}
(*p)["in p"] = 1 

make(map [string] int)符合您预期的原因是声明了地图并对其进行了初始化.

The reason make(map[string]int) does what you expect is that the map is declared and initialized.

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