bridge Мост (англ. Bridge) — структурный шаблон проектирования, используемый в проектировании программного обеспечения чтобы “разделять абстракцию и реализацию так, чтобы они могли изменяться независимо”. Шаблон мост использует инкапсуляцию, агрегирование и может использовать наследование для того, чтобы разделить ответственность между классами.

Родственным шаблоном для Моста является шаблон Адаптер, который объединяет связанные части системы и предоставляет простой интерфейс.

У нас есть филиалы в штатах и Европе. У каждого из регионов разная валюта. И подсчёты прибыли тоже производятся по-разному. Но наши CashBox всегда должны быть CashBox. Это и есть абстракция. Некоторые методы нашей абстракции, зависят от аргумента, который передаётся. Тип указан интерфейс CurrencyInterface. Интерфейс и есть реализация. Нам не нужно каждый раз наследовать родителя и менять что-то. У нас есть один тип, и мы знаем, как с ним работать. Как мы видим, что данный шаблон мы уже встречали в наших примерах.

  • Abstraction
    • AbstractCashBox.php 
                    
<?php

namespace DesignPatterns\Structural\Bridge\Abstraction;

use DesignPatterns\Structural\Bridge\Implementation\CurrencyInterface;

/**
 * Class AbstractCashBox
 * @package DesignPatterns\Structural\Bridge\Abstraction
 */
abstract class AbstractCashBox
{
    /**
     * @var CurrencyInterface
     */
    protected $defaultCurrency;

    /**
     * @var CurrencyInterface[]|float
     */
    protected $cash = [];

    /**
     * AbstractCashBox constructor.
     *
     * @param CurrencyInterface $currency
     */
    public function __construct(CurrencyInterface $currency)
    {
        $this->defaultCurrency = $currency;
    }

    /**
     * @return CurrencyInterface
     */
    public function getDefaultCurrency(): CurrencyInterface
    {
        return $this->defaultCurrency;
    }

    /**
     * @return float
     */
    abstract public function getCashInCashBox(): float;

    /**
     * @param CurrencyInterface $currency
     *
     * @return void
     */
    abstract public function setCash(CurrencyInterface $currency);
}
    • EuropeCashBox.php 
                    
<?php

namespace DesignPatterns\Structural\Bridge\Abstraction;

use DesignPatterns\Structural\Bridge\Implementation\CurrencyInterface;

/**
 * Class EuropeCashBox
 * @package DesignPatterns\Structural\Bridge\Abstraction
 */
class EuropeCashBox extends AbstractCashBox
{
    /**
     * @return float
     */
    public function getCashInCashBox(): float
    {
        return array_sum($this->cash);
    }

    /**
     * @param CurrencyInterface $currency
     *
     * @return void
     */
    public function setCash(CurrencyInterface $currency)
    {
        $defaultCurrencyRate = $this->defaultCurrency->getCurrencyRate();

        array_push($this->cash, ($currency->getSum() * $defaultCurrencyRate) / $currency->getCurrencyRate());
    }
}
    • UsaCashBox.php 
                    
<?php

namespace DesignPatterns\Structural\Bridge\Abstraction;

use DesignPatterns\Structural\Bridge\Implementation\CurrencyInterface;

/**
 * Class UsaCashBox
 * @package DesignPatterns\Structural\Bridge\Abstraction
 */
class UsaCashBox extends AbstractCashBox
{
    /**
     * @return float
     */
    public function getCashInCashBox(): float
    {
        $result = 0.0;

        $defaultCurrencyRate = $this->defaultCurrency->getCurrencyRate();

        foreach ($this->cash as $cash) {
            $result += ($cash->getSum() * $defaultCurrencyRate) / $cash->getCurrencyRate();
        }

        return $result;
    }

    /**
     * @param CurrencyInterface $currency
     *
     * @return void
     */
    public function setCash(CurrencyInterface $currency)
    {
        array_push($this->cash, $currency);
    }
}
  • Implementation
    • AbstractCurrency.php 
                    
<?php

namespace DesignPatterns\Structural\Bridge\Implementation;

/**
 * Class AbstractCurrency
 * @package DesignPatterns\Structural\Bridge\Implementation
 */
abstract class AbstractCurrency implements CurrencyInterface
{
    /**
     * @var string
     */
    protected $symbol;

    /**
     * @var float
     */
    protected $sumCash = 0.0;

    /**
     * AbstractCurrency constructor.
     *
     * @param float $sumCash
     */
    public function __construct(float $sumCash = null)
    {
        if ($sumCash) {
            $this->sumCash = $sumCash;
        }
    }

    /**
     * @return string
     */
    public function getCurrencySymbol(): string
    {
        return $this->symbol;
    }

    /**
     * @return float
     */
    public function getCurrencyRate(): float
    {
        return static::CURRENCY_RATE;
    }

    /**
     * @return float
     */
    public function getSum(): float
    {
        return $this->sumCash;
    }
}
    • CurrencyInterface.php 
                    
<?php
namespace DesignPatterns\Structural\Bridge\Implementation;

/**
 * Interface CurrencyInterface
 * @package DesignPatterns\Structural\Bridge\Implementation
 */
interface CurrencyInterface
{
    /**
     * CurrencyInterface constructor.
     *
     * @param float $sumCash
     */
    public function __construct(float $sumCash);

    /**
     * @return string
     */
    public function getCurrencySymbol(): string;

    /**
     * @return float
     */
    public function getCurrencyRate(): float;

    /**
     * @return float
     */
    public function getSum(): float;
}
    • DollarCurrency.php 
                    
<?php

namespace DesignPatterns\Structural\Bridge\Implementation;

/**
 * Class DollarCurrency
 * @package DesignPatterns\Structural\Bridge\Implementation
 */
class DollarCurrency extends AbstractCurrency
{
    /**
     * @var string
     */
    protected $symbol = '$';

    /**
     * @var float
     */
    const CURRENCY_RATE = 2.0;
}
    • EuroCurrency.php 
                    
<?php

namespace DesignPatterns\Structural\Bridge\Implementation;

/**
 * Class EuroCurrency
 * @package DesignPatterns\Structural\Bridge\Implementation
 */
class EuroCurrency extends AbstractCurrency
{
    /**
     * @var string
     */
    protected $symbol = '€';

    /**
     * @var float
     */
    const CURRENCY_RATE = 1;
}

    Test case:

    BridgeTest.php 
      
<?php
namespace DesignPatterns\Tests\Structural\Bridge;

use DesignPatterns\Structural\Bridge\Abstraction\EuropeCashBox;
use DesignPatterns\Structural\Bridge\Abstraction\UsaCashBox;
use DesignPatterns\Structural\Bridge\Implementation\CurrencyInterface;
use DesignPatterns\Structural\Bridge\Implementation\DollarCurrency;
use DesignPatterns\Structural\Bridge\Implementation\EuroCurrency;
use PHPUnit_Framework_TestCase;

class BridgeTest extends PHPUnit_Framework_TestCase
{
    public function testDollarCurrencyInstanceOfCurrencyInterface()
    {
        $dollar = new DollarCurrency();
        $this->assertInstanceOf('DesignPatterns\Structural\Bridge\Implementation\CurrencyInterface', $dollar);

        return $dollar;
    }

    /**
     * @depends testDollarCurrencyInstanceOfCurrencyInterface
     *
     * @param CurrencyInterface $dollar
     */
    public function testDollarGetSymbol(CurrencyInterface $dollar)
    {
        $this->assertEquals('$', $dollar->getCurrencySymbol());
    }

    /**
     * @depends testDollarCurrencyInstanceOfCurrencyInterface
     *
     * @param CurrencyInterface $dollar
     */
    public function testDollarGetRate(CurrencyInterface $dollar)
    {
        $this->assertEquals(DollarCurrency::CURRENCY_RATE, $dollar->getCurrencyRate());
    }

    public function testDollarGetSum()
    {
        $val = 234.24;
        $dollar = new DollarCurrency($val);

        $this->assertEquals($val, $dollar->getSum());
    }

    public function testEuroCurrencyInstanceOfCurrencyInterface()
    {
        $euro = new EuroCurrency();
        $this->assertInstanceOf('DesignPatterns\Structural\Bridge\Implementation\CurrencyInterface', $euro);

        return $euro;
    }

    /**
     * @depends testEuroCurrencyInstanceOfCurrencyInterface
     *
     * @param CurrencyInterface $euro
     */
    public function testEuroGetSymbol(CurrencyInterface $euro)
    {
        $this->assertEquals('€', $euro->getCurrencySymbol());
    }

    /**
     * @depends testEuroCurrencyInstanceOfCurrencyInterface
     *
     * @param CurrencyInterface $euro
     */
    public function testEuroGetRate(CurrencyInterface $euro)
    {
        $this->assertEquals(EuroCurrency::CURRENCY_RATE, $euro->getCurrencyRate());
    }

    public function testEuroGetSum()
    {
        $val = 2555.24;
        $dollar = new EuroCurrency($val);

        $this->assertEquals($val, $dollar->getSum());
    }

    public function testUsaCashBoxInstanceOfAbstractCashBox()
    {
        $dollar = new DollarCurrency();
        $usaCashBox = new UsaCashBox($dollar);

        $this->assertInstanceOf('DesignPatterns\Structural\Bridge\Abstraction\AbstractCashBox', $usaCashBox);
    }

    public function testEuroCashBoxInstanceOfAbstractCashBox()
    {
        $euro = new EuroCurrency();
        $euroCashBox = new EuropeCashBox($euro);

        $this->assertInstanceOf('DesignPatterns\Structural\Bridge\Abstraction\AbstractCashBox', $euroCashBox);
    }

    public function testUsaCashBoxGetCashInCashBox()
    {
        $dollar = new DollarCurrency();

        $fiveDollars = new DollarCurrency(5);
        $sixDollars = new DollarCurrency(6);
        $tenEuros = new EuroCurrency(10);

        $usaCashBox = new UsaCashBox($dollar);

        $usaCashBox->setCash($fiveDollars);
        $this->assertEquals($fiveDollars->getSum(), $usaCashBox->getCashInCashBox());

        $usaCashBox->setCash($sixDollars);
        $this->assertEquals(
            $fiveDollars->getSum() + $sixDollars->getSum(),
            $usaCashBox->getCashInCashBox()
        );

        $usaCashBox->setCash($tenEuros);
        $defaultCurrencyRate = $usaCashBox->getDefaultCurrency()->getCurrencyRate();

        $this->assertEquals(
            $fiveDollars->getSum()
            + $sixDollars->getSum()
            + (($tenEuros->getSum() * $defaultCurrencyRate) / $tenEuros->getCurrencyRate()),
            $usaCashBox->getCashInCashBox()
        );
    }
}