Insert or update an element in map m:

m[key] = elem

Retrieve an element:

elem = m[key]

Delete an element:

delete(m, key)

Test that a key is present with a two-value assignment:

elem, ok = m[key]

If key is in m, ok is true. If not, ok is false and elem is the zero value for the map‘s element type.

Similarly, when reading from a map if the key is not present the result is the zero value for the map‘s element type.

package main import "fmt"func main() {    m := make(map[string]int)    m["Answer"] = 42    fmt.Println("The value:", m["Answer"])    m["Answer"] = 48    fmt.Println("The value:", m["Answer"])    v, ok := m["Answer"]    fmt.Println("The value:", v, "Present?", ok)    delete(m, "Answer")    fmt.Println("The value:", m["Answer"])    v2, ok2 := m["Answer"]    fmt.Println("The value:", v2, "Present?", ok2)}

好变态的map用法，真不知道google是怎怎么想的

A Tour of Go Mutating Maps