Map

声明和初始化

func main() {
    // 声明、初始化、赋值分三步
    var map1 map[string]int
    // map1["one"] = 1 // 此时不能直接使用
    map1 = make(map[string]int)
    map1["one"] = 1

    // 声明+初始化、赋值分两步
    var map2 = make(map[string]int)
    map2["two"] = 2

    // 声明+初始化+赋值
    map3 := map[string]int{"three": 3}

    fmt.Printf("%T %v\n", map1, map1) // map[string]int map[one:1]
    fmt.Printf("%T %v\n", map2, map2) // map[string]int map[two:2]
    fmt.Printf("%T %v\n", map3, map3) // map[string]int map[three:3]
}

判断map中是否存在某个key

func main(){
    map4 := map[string]int{
        "one":   1,
        "two":   2,
        "three": 3,
    }

    v, ok := map4["one"]
    if ok {
        fmt.Println(v)
    } else {
        fmt.Println("the key is not exist")
    }
}

map是引用类型

func main(){
    fmt.Println(map4) // map[one:1 three:3 two:2]
    map5 := map4
    map5["one"] = 4
    fmt.Println(map4) // map[one:4 three:3 two:2]
}

元素为map类型的切片

func main(){
    var mapSlice = make([]map[string]string, 3)
    fmt.Println(mapSlice) // [map[] map[] map[]]
    mapSlice[0] = make(map[string]string)
    mapSlice[0]["name"] = "mike"
    mapSlice[0]["sex"] = "male"
    mapSlice[0]["city"] = "beijing"
    fmt.Println(mapSlice) // [map[city:beijing name:mike sex:male] map[] map[]]
}

值为切片类型的map

func main(){
    var sliceMap = make(map[string][]string)
    sliceMap["chinese"] = []string{"beijing", "shanghai"}
    sliceMap["japanese"] = []string{"tokyo", "osaka"}
    fmt.Println(sliceMap) // map[chinese:[beijing shanghai] japanese:[tokyo osaka]]
}