golang フレームワークのソースコード設計パターンの探索

package main

import (
    "fmt"
    "sync"
)

type Singleton struct {}

var (
    once sync.Once
    instance *Singleton
)

func GetInstance() *Singleton {
    once.Do(func() {
        instance = &Singleton{}
    })
    return instance
}

func main() {
    instance1 := GetInstance()
    instance2 := GetInstance()
    fmt.Println(instance1 == instance2) // 输出: true
}

package main

type Animal interface {
    Speak() string
}

type Dog struct {}

func (d *Dog) Speak() string {
    return "Woof!"
}

type Cat struct {}

func (c *Cat) Speak() string {
    return "Meow!"
}

type AnimalFactory struct {}

func (f *AnimalFactory) CreateAnimal(name string) (Animal, error) {
    switch name {
        case "dog":
            return &Dog{}, nil
        case "cat":
            return &Cat{}, nil
        
        default:
            return nil, fmt.Errorf("Unsupported animal type: %s", name)
    }
}

func main() {
    factory := AnimalFactory{}
    dog, _ := factory.CreateAnimal("dog")
    cat, _ := factory.CreateAnimal("cat")
    fmt.Println(dog.Speak()) // 输出: "Woof!"
    fmt.Println(cat.Speak()) // 输出: "Meow!"
}

package main

import "fmt"

type Observable struct {
    observers []Observer
    state int
}

func (o *Observable) AddObserver(observer Observer) {
    o.observers = append(o.observers, observer)
}

func (o *Observable) NotifyObservers() {
    for _, observer := range o.observers {
        observer.Update(o.state)
    }
}

type Observer interface {
    Update(state int)
}

type ConcreteObserver1 struct {}

func (c *ConcreteObserver1) Update(state int) {
    fmt.Println("Observer 1:", state)
}

type ConcreteObserver2 struct {}

func (c *ConcreteObserver2) Update(state int) {
    fmt.Println("Observer 2:", state)
}

func main() {
    observable := Observable{}
    observer1 := ConcreteObserver1{}
    observer2 := ConcreteObserver2{}
    observable.AddObserver(observer1)
    observable.AddObserver(observer2)
    observable.state = 10
    observable.NotifyObservers()  // 输出: Observer 1: 10, Observer 2: 10
}