mapgotcha.go

package main

import "fmt"

type person struct {
	Name string
	Age  int
}

func main() {
	students := make(map[int]person)
	students[0] = person{Name: "John"}
	fmt.Printf("students[0] = %+v\n", students[0]) // {Name:John Age:0}
	// students[0].Age = 22 // error: cannot assign to struct field
	john := students[0]
	john.Age = 22
	fmt.Printf("students[0] = %+v\n", students[0]) // {Name:John Age:0}
	students[0] = john
	fmt.Printf("students[0] = %+v\n", students[0]) // {Name:John Age:22}

	pstudents := make(map[int]*person)
	pstudents[0] = &person{Name: "Criss"}
	fmt.Printf("students[0] = %+v\n", pstudents[0]) // &{Name:Criss Age:0}
	pstudents[0].Age = 33
	fmt.Printf("students[0] = %+v\n", pstudents[0]) // &{Name:Criss Age:33}
}