pointer_in_goroutine.go

package main

import (
	"fmt"
	"sync"
)

type Person struct {
	Name string
}

func main() {
	people := []Person{
		{Name: "taro"},
		{Name: "jiro"},
		{Name: "hana"},
	}

	var wg sync.WaitGroup
	fmt.Println("==PASS VALUE===")

	for _, person := range people {
		wg.Add(1)

		fmt.Printf("address of an slice: %p\n", &people)

		// こうするとperson(要素)のアドレスが変わる(新しいローカル変数が作成されるため)
		// person := person

		go func(p Person) {
			fmt.Println(p.Name)
			wg.Done()
		}(person)
		fmt.Printf("address of an element: %p\n", &person)

	}
	wg.Wait()

	fmt.Println("==PASS POINTER==")
	for _, person := range people {
		wg.Add(1)
		go func(p *Person) {
			fmt.Println(p.Name)
			wg.Done()
		}(&person)
	}
	wg.Wait()

	fmt.Println("==LOOP WITH INDEX==")
	for i := range people {
		wg.Add(1)
		go func(p *Person) {
			fmt.Println(p.Name)
			wg.Done()
		}(&people[i])
	}
	wg.Wait()
}

// ==PASS VALUE===
// address of an slice: 0x40c0e0
// address of an element: 0x40e130
// address of an slice: 0x40c0e0
// address of an element: 0x40e130
// address of an slice: 0x40c0e0
// address of an element: 0x40e130
// hana
// taro
// jiro
// ==PASS POINTER==
// hana
// hana
// hana
// ==LOOP WITH INDEX==
// hana
// taro
// jiro