langToMap.go

langToMap.go

package main

import (
	"fmt"
)

type Language struct {
	ID   int
	Code string
}

func MakeMap1(langs []*Language) map[int]string {
	var m = map[int]string{}
	for _, l := range langs {
		m[l.ID] = l.Code
	}
	return m
}

type Langs []*Language

func (langs Langs) MakeMap2() map[int]string {
	var m = map[int]string{}
	for _, l := range langs {
		m[l.ID] = l.Code
	}
	return m
}

type Langs2 = []*Language

// Fail: invalid receiver type []*Language ([]*Language is an unnamed type)
func (langs Langs2) MakeMap3() map[int]string {
	var m = map[int]string{}
	for _, l := range langs {
		m[l.ID] = l.Code
	}
	return m
}

func main() {
	langs := []*Language{
		&Language{
			ID:   1,
			Code: "en",
		},
		&Language{
			ID:   2,
			Code: "ja",
		},
	}

	m1 := MakeMap1(langs)
	fmt.Printf("Map 1===============\n")
	for k, v := range m1 {
		fmt.Printf("%d:%s\n", k, v)
	}
	fmt.Printf("====================\n")

	ls1 := Langs(langs)
	m2 := ls1.MakeMap2()
	fmt.Printf("Map 2===============\n")
	for k, v := range m2 {
		fmt.Printf("%d:%s\n", k, v)
	}
	fmt.Printf("====================\n")

	// Fail: langs.MakeMap2 undefined (type []*Language has no field or method MakeMap2)
	// m3 := langs.MakeMap2()
	// fmt.Printf("Map 3===============\n")
	// for k, v := range m3 {
	// 	fmt.Printf("%d:%s\n", k, v)
	// }
	// fmt.Printf("====================\n")

	// Fail: langs.MakeMap2 undefined (type []*Language has no field or method MakeMap2)
	m3 := langs.MakeMap2()
	fmt.Printf("Map 3===============\n")
	for k, v := range m3 {
		fmt.Printf("%d:%s\n", k, v)
	}
	fmt.Printf("====================\n")
}