Design Patterns | Singleton

Creational pattern - Singleton

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package cards

import (
	"sync"
)

type holder map[string]string

var storeObject holder
var once sync.Once

func New() holder {
	once.Do(func() {
		storeObject = make(holder)
	})
	return storeObject
}

Here we define package cards, that encapsulates relationship between card number and and owner of a card. It’s concurency free function func New() code, that creates object only if it’s not initialized before.

Below you can find the basic usage of this pattern:

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package main

import (
	"fmt"

	"cards"
)

func main() {
	store := cards.New()
	store["1111-2222-3333-4444"] = "John Doe"
	store2 := cards.New()
	fmt.Println(store2["1111-2222-3333-4444"])
}

Sample output of program shows that there are no another instance was created.