3.10. Strategy

3.10.1. Terminology:

  • Context
  • Strategy
  • Concrete Strategy

3.10.2. Purpose

To separate strategies and to enable fast switching between them. Alsothis pattern is a good alternative to inheritance (instead of having anabstract class that is extended).

3.10.3. Examples

  • sorting a list of objects, one strategy by date, the other by id
  • simplify unit testing: e.g. switching between file and in-memorystorage

3.10.4. UML Diagram

Alt Strategy UML Diagram

3.10.5. Code

You can also find this code on GitHub

Context.php

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

ComparatorInterface.php

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

DateComparator.php

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

IdComparator.php

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

3.10.6. Test

Tests/StrategyTest.php

  1. <?php
  2.  
  3. namespace DesignPatterns\Behavioral\Strategy\Tests;
  4.  
  5. use DesignPatterns\Behavioral\Strategy\Context;
  6. use DesignPatterns\Behavioral\Strategy\DateComparator;
  7. use DesignPatterns\Behavioral\Strategy\IdComparator;
  8. use PHPUnit\Framework\TestCase;
  9.  
  10. class StrategyTest extends TestCase
  11. {
  12.     public function provideIntegers()
  13.     {
  14.         return [
  15.             [
  16.                 [['id' => 2], ['id' => 1], ['id' => 3]],
  17.                 ['id' => 1],
  18.             ],
  19.             [
  20.                 [['id' => 3], ['id' => 2], ['id' => 1]],
  21.                 ['id' => 1],
  22.             ],
  23.         ];
  24.     }
  25.  
  26.     public function provideDates()
  27.     {
  28.         return [
  29.             [
  30.                 [['date' => '2014-03-03'], ['date' => '2015-03-02'], ['date' => '2013-03-01']],
  31.                 ['date' => '2013-03-01'],
  32.             ],
  33.             [
  34.                 [['date' => '2014-02-03'], ['date' => '2013-02-01'], ['date' => '2015-02-02']],
  35.                 ['date' => '2013-02-01'],
  36.             ],
  37.         ];
  38.     }
  39.  
  40.     /**
  41.      * @dataProvider provideIntegers
  42.      *
  43.      * @param array $collection
  44.      * @param array $expected
  45.      */
  46.     public function testIdComparator($collection, $expected)
  47.     {
  48.         $obj = new Context(new IdComparator());
  49.         $elements = $obj->executeStrategy($collection);
  50.  
  51.         $firstElement = array_shift($elements);
  52.         $this->assertEquals($expected, $firstElement);
  53.     }
  54.  
  55.     /**
  56.      * @dataProvider provideDates
  57.      *
  58.      * @param array $collection
  59.      * @param array $expected
  60.      */
  61.     public function testDateComparator($collection, $expected)
  62.     {
  63.         $obj = new Context(new DateComparator());
  64.         $elements = $obj->executeStrategy($collection);
  65.  
  66.         $firstElement = array_shift($elements);
  67.         $this->assertEquals($expected, $firstElement);
  68.     }
  69. }