映射(Maps)

映射（maps）是Go中的内置关联数据类型（在其他语言中有时称为哈希或字典）。

Maps are Go’s built-in associative data type (sometimes called hashes or dicts in other languages).

要创建一个空映射，可以使用内置的make函数：make(map[key-type]val-type)。

To create an empty map, use the builtin make: make(map[key-type]val-type).

package main

func main() {
	m := make(map[string]int)
}

package main

func main() {
	m := make(map[string]int)
}

使用常规的name[key] = val语法设置键值对。

Set key/value pairs using typical name[key] = val syntax.

package main

func main() {
	m := make(map[string]int)
	m["k1"] = 7 
	m["k2"] = 13
  fmt.Println("map:", m)
}

package main

func main() {
	m := make(map[string]int)
	m["k1"] = 7 
	m["k2"] = 13
  fmt.Println("map:", m)
}

使用fmt.Println等将映射打印出来会显示所有的键值对。

Printing a map with e.g. fmt.Println will show all of its key/value pairs.

package main

func main() {
	m := make(map[string]int)
	m["k1"] = 7
	m["k2"] = 13
  fmt.Println("map:", m)  
	// map: map[k1:7 k2:13]
}

package main

func main() {
	m := make(map[string]int)
	m["k1"] = 7
	m["k2"] = 13
  fmt.Println("map:", m)  
	// map: map[k1:7 k2:13]
}

使用name[key]获取键对应的值。

Get a value for a key with name[key].

package main

import "fmt"

func main() {

	// ... 省略重复代码

	v1 := m["k1"]
	fmt.Println("v1:", v1)
	// v1: 7
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	v1 := m["k1"]
	fmt.Println("v1:", v1)
	// v1: 7
}

如果键不存在，则会返回值类型的零值。

If the key doesn’t exist, the zero value of the value type is returned.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	v3 := m["k3"]
	fmt.Println("v3:", v3)
	// v3: 0
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	v3 := m["k3"]
	fmt.Println("v3:", v3)
	// v3: 0
}

调用内置的len函数可以返回映射中键值对的数量。

The builtin len returns the number of key/value pairs when called on a map.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	fmt.Println("len:", len(m))
	// len: 2
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	fmt.Println("len:", len(m))
	// len: 2
}

使用内置的delete函数可以从映射中删除键值对。

The builtin delete removes key/value pairs from a map.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	delete(m, "k2")
	fmt.Println("map:", m)
	// map: map[k1:7]
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	delete(m, "k2")
	fmt.Println("map:", m)
	// map: map[k1:7]
}

要从映射中删除所有的键值对，使用内置的clear函数。

To remove all key/value pairs from a map, use the clear builtin.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	clear(m)
	fmt.Println("map:", m)
	// map: map[]
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	clear(m)
	fmt.Println("map:", m)
	// map: map[]
}

从映射中获取值时，可选的第二个返回值表示键是否存在于映射中。这可以用于区分缺失的键和具有零值（如0或""）的键。在这里，我们不需要值本身，所以使用空白标识符_将其忽略掉。

The optional second return value when getting a value from a map indicates if the key was present in the map. This can be used to disambiguate between missing keys and keys with zero values like 0 or "". Here we didn’t need the value itself, so we ignored it with the blank identifier _.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	_, prs := m["k2"]
	fmt.Println("prs:", prs)
	// prs: false
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	_, prs := m["k2"]
	fmt.Println("prs:", prs)
	// prs: false
}

还可以使用以下语法在同一行中声明和初始化新的映射。

You can also declare and initialize a new map in the same line with this syntax.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("map:", n)
	// map: map[bar:2 foo:1]
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("map:", n)
	// map: map[bar:2 foo:1]
}

maps包中包含了一些对映射非常有用的实用函数。

The maps package contains a number of useful utility functions for maps.

package main

import "fmt"

func main() {

	// ... 省略重复代码

	
	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("map:", n)
	// map: map[bar:2 foo:1]
  
	n2 := map[string]int{"foo": 1, "bar": 2}
	if maps.Equal(n, n2) {
		fmt.Println("n == n2")
		// n == n2
	}
}

package main

import "fmt"

func main() {

	// ... 省略重复代码

	
	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("map:", n)
	// map: map[bar:2 foo:1]
  
	n2 := map[string]int{"foo": 1, "bar": 2}
	if maps.Equal(n, n2) {
		fmt.Println("n == n2")
		// n == n2
	}
}

请注意，使用fmt.Println打印映射时，它的形式是map[k:v k:v]。

Note that maps appear in the form map[k:v k:v] when printed with fmt.Println.

运行

package main

import (
	"fmt"
	"maps"
)

func main() {
	m := make(map[string]int)
	m["k1"] = 7
	m["k2"] = 13
	fmt.Println("map:", m)

	v1 := m["k1"]
	fmt.Println("v1:", v1)
	v3 := m["key3"]
	fmt.Println("v3:", v3)

	fmt.Println("len:", len(m))

	delete(m, "k2")
	fmt.Println("map:", m)

	clear(m)
	fmt.Println("map:", m)

	_, prs := m["k2"]
	fmt.Println("prs:", prs)

	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("map:", n)

	n2 := map[string]int{"foo": 1, "bar": 2}
	if maps.Equal(n, n2) {
		fmt.Println("n == n2")
	}
}

package main

import (
	"fmt"
	"maps"
)

func main() {
	m := make(map[string]int)
	m["k1"] = 7
	m["k2"] = 13
	fmt.Println("map:", m)

	v1 := m["k1"]
	fmt.Println("v1:", v1)
	v3 := m["key3"]
	fmt.Println("v3:", v3)

	fmt.Println("len:", len(m))

	delete(m, "k2")
	fmt.Println("map:", m)

	clear(m)
	fmt.Println("map:", m)

	_, prs := m["k2"]
	fmt.Println("prs:", prs)

	n := map[string]int{"foo": 1, "bar": 2}
	fmt.Println("map:", n)

	n2 := map[string]int{"foo": 1, "bar": 2}
	if maps.Equal(n, n2) {
		fmt.Println("n == n2")
	}
}

bash

go run 10-maps.go

# map: map[k1:7 k2:13]
# v1: 7
# v3: 0
# len: 2
# map: map[k1:7]
# map: map[]
# prs: false
# map: map[bar:2 foo:1]
# n == n2

go run 10-maps.go

# map: map[k1:7 k2:13]
# v1: 7
# v3: 0
# len: 2
# map: map[k1:7]
# map: map[]
# prs: false
# map: map[bar:2 foo:1]
# n == n2

运行 ​

运行