单例模式

这个模式被认为是反模式。为了更好的测试性和维护性，请使用依赖注入。

<?php
namespace DesignPatterns\Creational\Singleton;

final class Singleton
{
    private static $instance;

    public static function getInstance(): Singleton
    {
        if (null === static::$instance) {
            static::$instance = new static();
        }

        return static::$instance;
    }

    private function __construct()
    {
    }

    private function __clone()
    {
    }

    private function __wakeup()
    {
    }
}

<?php

namespace DesignPatterns\Creational\Singleton\Tests;

use DesignPatterns\Creational\Singleton\Singleton;
use PHPUnit\Framework\TestCase;

class SingletonTest extends TestCase
{
    public function testUniqueness()
    {
        $firstCall = Singleton::getInstance();
        $secondCall = Singleton::getInstance();

        $this->assertInstanceOf(Singleton::class, $firstCall);
        $this->assertSame($firstCall, $secondCall);
    }
}