模式定义

与单例模式类似，只是多例模式能够返回多个实例；

应用场景

• 多个数据库连接（mysql、MongoDb、SQLite）
• 多种日志记录

UML类图

代码实现

Multiton.php

<?php

namespace DesignPatterns\Creational\Multiton;

final class Multiton
{
    const INSTANCE_1 = '1';
    const INSTANCE_2 = '2';

    /**
     * @var Multiton[]
     */
    private static $instances = [];

    /**
     * this is private to prevent from creating arbitrary instances
     */
    private function __construct()
    {
    }

    public static function getInstance(string $instanceName): Multiton
    {
        if (!isset(self::$instances[$instanceName])) {
            self::$instances[$instanceName] = new self();
        }

        return self::$instances[$instanceName];
    }

    /**
     * prevent instance from being cloned
     */
    private function __clone()
    {
    }

    /**
     * prevent instance from being unserialized
     */
    private function __wakeup()
    {
    }
}

MultitonTest.php

<?php

namespace DesignPatterns\Creational\Multition\Tests;

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

class MultitonTest extends TestCase
{
    public function testUniqueness()
    {
        $firstCall = Multiton::getInstance(Multiton::INSTANCE_1);
        $secondCall = Multiton::getInstance(Multiton::INSTANCE_1);

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

    public function testUniquenessForEveryInstance()
    {
        $firstCall = Multiton::getInstance(Multiton::INSTANCE_1);
        $secondCall = Multiton::getInstance(Multiton::INSTANCE_2);

        $this->assertInstanceOf(Multiton::class, $firstCall);
        $this->assertInstanceOf(Multiton::class, $secondCall);
        $this->assertNotSame($firstCall, $secondCall);
    }
}