策略模式（Strategy）

术语

  • 上下文
  • 策略
  • 具体策略

目的

分离「策略」并使他们之间能互相快速切换。此外，这种模式是一种不错的继承替代方案（替代使用扩展抽象类的方式）。

例子

  • 对一个对象列表进行排序，一种按照日期，一种按照 id
  • 简化版的的单元测试：例如，在使用文件存储和内存存储之间互相切换

UML 类图

file

代码

你可以在 GitHub 上找到这个代码。

Context.php

  2. <?php
  4. namespace DesignPatterns\Behavioral\Strategy;
  6. class Context
  7. {
  8.     /**
  9.      * @var ComparatorInterface
  10.      */
  11.     private $comparator;
  13.     public function __construct(ComparatorInterface $comparator)
  14.     {
  15.         $this->comparator = $comparator;
  16.     }
  18.     public function executeStrategy(array $elements) : array
  19.     {
  20.         uasort($elements, [$this->comparator, 'compare']);
  22.         return $elements;
  23.     }
  24. }

ComparatorInterface.php

  2. <?php
  4. namespace DesignPatterns\Behavioral\Strategy;
  6. interface ComparatorInterface
  7. {
  8.     /**
  9.      * @param mixed $a
  10.      * @param mixed $b
  11.      *
  12.      * @return int
  13.      */
  14.     public function compare($a, $b): int;
  15. }

DateComparator.php

  2. <?php
  4. namespace DesignPatterns\Behavioral\Strategy;
  6. class DateComparator implements ComparatorInterface
  7. {
  8.     /**
  9.      * @param mixed $a
  10.      * @param mixed $b
  11.      *
  12.      * @return int
  13.      */
  14.     public function compare($a, $b): int
  15.     {
  16.         $aDate = new \DateTime($a['date']);
  17.         $bDate = new \DateTime($b['date']);
  19.         return $aDate <=> $bDate;
  20.     }
  21. }

IdComparator.php

  2. <?php
  4. namespace DesignPatterns\Behavioral\Strategy;
  6. class IdComparator implements ComparatorInterface
  7. {
  8.     /**
  9.      * @param mixed $a
  10.      * @param mixed $b
  11.      *
  12.      * @return int
  13.      */
  14.     public function compare($a, $b): int
  15.     {
  16.         return $a['id'] <=> $b['id'];
  17.     }
  18. }

测试

Tests/StrategyTest.php

  2. <?php
  4. namespace DesignPatterns\Behavioral\Strategy\Tests;
  6. use DesignPatterns\Behavioral\Strategy\Context;
  7. use DesignPatterns\Behavioral\Strategy\DateComparator;
  8. use DesignPatterns\Behavioral\Strategy\IdComparator;
  9. use PHPUnit\Framework\TestCase;
  11. class StrategyTest extends TestCase
  12. {
  13.     public function provideIntegers()
  14.     {
  15.         return [
  16.             [
  17.                 [['id' => 2], ['id' => 1], ['id' => 3]],
  18.                 ['id' => 1],
  19.             ],
  20.             [
  21.                 [['id' => 3], ['id' => 2], ['id' => 1]],
  22.                 ['id' => 1],
  23.             ],
  24.         ];
  25.     }
  27.     public function provideDates()
  28.     {
  29.         return [
  30.             [
  31.                 [['date' => '2014-03-03'], ['date' => '2015-03-02'], ['date' => '2013-03-01']],
  32.                 ['date' => '2013-03-01'],
  33.             ],
  34.             [
  35.                 [['date' => '2014-02-03'], ['date' => '2013-02-01'], ['date' => '2015-02-02']],
  36.                 ['date' => '2013-02-01'],
  37.             ],
  38.         ];
  39.     }
  41.     /**
  42.      * @dataProvider provideIntegers
  43.      *
  44.      * @param array $collection
  45.      * @param array $expected
  46.      */
  47.     public function testIdComparator($collection, $expected)
  48.     {
  49.         $obj = new Context(new IdComparator());
  50.         $elements = $obj->executeStrategy($collection);
  52.         $firstElement = array_shift($elements);
  53.         $this->assertEquals($expected, $firstElement);
  54.     }
  56.     /**
  57.      * @dataProvider provideDates
  58.      *
  59.      * @param array $collection
  60.      * @param array $expected
  61.      */
  62.     public function testDateComparator($collection, $expected)
  63.     {
  64.         $obj = new Context(new DateComparator());
  65.         $elements = $obj->executeStrategy($collection);
  67.         $firstElement = array_shift($elements);
  68.         $this->assertEquals($expected, $firstElement);
  69.     }
  70. }