1. 设计模式
  2. 行为型模式
  3. 策略模式

策略模式

术语

  • Context：上下文
  • Strategy：策略
  • Concrete Strategy：具体策略

目的

分离不同的策略，并实现各种策略之间的快速切换。另外，策略模式也是继承的一个很好的替代方案（而不是拥有一个被扩展的抽象类）。

使用场景

  • 对一组对象进行排序，一种按时间排序，其余的按 ID 排序
  • 简化单元测试：比如，在文件存储和内存存储之间切换时

UML 类图

策略模式类图

代码

Context.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\Strategy;

class Context
{
    private Comparator $comparator;

    public function __construct(Comparator $comparator)
    {
        $this->comparator = $comparator;
    }

    public function executeStrategy(array $elements): array
    {
        uasort($elements, [$this->comparator, 'compare']);

        return $elements;
    }
}

Comparator.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\Strategy;

interface Comparator
{
    /**
     * @param mixed $a
     * @param mixed $b
     *
     * @return int
     */
    public function compare($a, $b): int;
}

DateComparator.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\Strategy;

use DateTime;

class DateComparator implements Comparator
{
    public function compare($a, $b): int
    {
        $aDate = new DateTime($a['date']);
        $bDate = new DateTime($b['date']);

        return $aDate <=> $bDate;
    }
}

IdComparator.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\Strategy;

class IdComparator implements Comparator
{
    public function compare($a, $b): int
    {
        return $a['id'] <=> $b['id'];
    }
}

测试

Tests/StrategyTest.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Behavioral\Strategy\Tests;

use DesignPatterns\Behavioral\Strategy\Context;
use DesignPatterns\Behavioral\Strategy\DateComparator;
use DesignPatterns\Behavioral\Strategy\IdComparator;
use PHPUnit\Framework\TestCase;

class StrategyTest extends TestCase
{
    public function provideIntegers()
    {
        return [
            [
                [['id' => 2], ['id' => 1], ['id' => 3]],
                ['id' => 1],
            ],
            [
                [['id' => 3], ['id' => 2], ['id' => 1]],
                ['id' => 1],
            ],
        ];
    }

    public function provideDates()
    {
        return [
            [
                [['date' => '2014-03-03'], ['date' => '2015-03-02'], ['date' => '2013-03-01']],
                ['date' => '2013-03-01'],
            ],
            [
                [['date' => '2014-02-03'], ['date' => '2013-02-01'], ['date' => '2015-02-02']],
                ['date' => '2013-02-01'],
            ],
        ];
    }

    /**
     * @dataProvider provideIntegers
     *
     * @param array $collection
     * @param array $expected
     */
    public function testIdComparator($collection, $expected)
    {
        $obj = new Context(new IdComparator());
        $elements = $obj->executeStrategy($collection);

        $firstElement = array_shift($elements);
        $this->assertSame($expected, $firstElement);
    }

    /**
     * @dataProvider provideDates
     *
     * @param array $collection
     * @param array $expected
     */
    public function testDateComparator($collection, $expected)
    {
        $obj = new Context(new DateComparator());
        $elements = $obj->executeStrategy($collection);

        $firstElement = array_shift($elements);
        $this->assertSame($expected, $firstElement);
    }
}
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