Singleton

Singleton pattern is the design where a class/structure only instantiate once and reused across the applications. This is commonly seen for global variable classes.

When to Use (Problem)

When the problem needs one and only one object instance of the class/structure.

Example (Solution)

Here is an example in Go for a package:

package main

import (

        "fmt"

        "sync"

var (

        instance *Singleton

        once     sync.Once

type Singleton struct {

        Data string

func GetSingleton() *Singleton {

        once.Do(func() {

                instance = &Singleton{

                        Data: "",

})

        return instance

func main() {

        s := GetSingleton()

        fmt.Printf("Print 1: %s\n", s.Data)

        s.Data = "Cron"

        s = GetSingleton()

        fmt.Printf("Print 2: %s\n", s.Data)

        s.Data = "Deux"

        s = GetSingleton()

        fmt.Printf("Print 3: %s\n", s.Data)

        s.Data = "Tres"

        s = GetSingleton()

        fmt.Printf("Print 4: %s\n", s.Data)

// Output:

// Print 1:

// Print 2: Cron

// Print 3: Deux

// Print 4: Tres

Usually, singleton requires the synchronized creation. You only need to synchronize the creation once and save the creation into a global variable. Then, at every needs, you just call in the global variable and use it.

Expected Outcome (Consequences)

A single instance object is created for the entire application.

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