unsafe_pointer_map.go

package main

import (
	"fmt"
	"reflect"
	"unsafe"
)

func Put(p unsafe.Pointer, key interface{}, value interface{}) {
	mapType := reflect.MapOf(reflect.TypeOf(key), reflect.TypeOf(value))
	mapValue := reflect.Indirect(reflect.NewAt(mapType, p))
	mapValue.SetMapIndex(reflect.ValueOf(key), reflect.ValueOf(value))
}

func main() {
	m := make(map[string]int)
	m["a"] = 10

	Put(unsafe.Pointer(&m), "b", 3)
	fmt.Printf("%v", m)
	// map[a:10 b:3]
}