How to expand golang's hashmap

Define hashmap variables

Since go language is a strongly typed language, hashmap is also typed, specifically reflected in key and value The type must be specified. For example, if you declare a key as string and value as a map of string, you need to do this. (Recommended learning: go)

var m map[string]string // 声明一个hashmap，还不能直接使用，必须使用make来初始化
m = make(map[string]string) // 初始化一个map
m = make(map[string]string, 3) // 初始化一个map并附带一个可选的初始bucket（非准确值，只是有提示意义）

m := map[string]string{} // 声明并初始化

m := make(map[string]string) // 使用make来初始化

get,set,delete

m := map[string]int
m["a"] = 1
fmt.Println(m["a"]) // 输出 1
// 如果访问一个不存在的key，返回类型默认值
fmt.Println(m["b"]) // 输出0
// 测试key是否存在
v, ok := m["b"]
if ok {
    ...
}
// 删除一个key
delete(m, "a")
迭代器
// 只迭代key
for k := range m {
    ...
}
// 同时迭代key-value
for k, v := range m {
    ...
}

During the iteration process, the map can be deleted and updated. The rules are as follows:

The iteration is unordered, and the order is the same as the insertion. Irrelevant

Delete a key during the iteration process. No matter whether it has been traversed or not, it will not be traversed to

. During the iteration process, a key is added. It is not sure whether it can be traversed to

.

Uninitialized maps can also be iterated

Others

The value of the map is not an address, which means that the syntax of &m["a"] is Illegal

len and cap can respectively obtain the number of kv and total capacity of the current map

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