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PHP 策略模式讲解和代码示例
策略是一种行为设计模式， 它将一组行为转换为对象， 并使其在原始上下文对象内部能够相互替换。
原始对象被称为上下文， 它包含指向策略对象的引用并将执行行为的任务分派给策略对象。 为了改变上下文完成其工作的方式， 其他对象可以使用另一个对象来替换当前链接的策略对象。
复杂度：******
流行度：******
使用示例： PHP 代码中经常使用策略模式， 特别是必须在运行时切换算法的情形中。 但是， PHP 从 2009 年开始支持匿名函数， 以其为代表的强大竞争对手挑战着模式的使用。
识别方法： 策略模式可以通过允许嵌套对象完成实际工作的方法以及允许将该对象替换为不同对象的设置器来识别。
概念示例
本例说明了策略设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
了解该模式的结构后， 你可以更容易地理解下面基于真实世界的 PHP 应用案例。
** index.php: 概念示例
<?php
namespace RefactoringGuru\Strategy\Conceptual;
/**
* The Context defines the interface of interest to clients.
*/
class Context
{
/**
* @var Strategy The Context maintains a reference to one of the Strategy
* objects. The Context does not know the concrete class of a strategy. It
* should work with all strategies via the Strategy interface.
*/
private $strategy;
/**
* Usually, the Context accepts a strategy through the constructor, but also
* provides a setter to change it at runtime.
*/
public function __construct(Strategy $strategy)
{
$this->strategy = $strategy;
}
/**
* Usually, the Context allows replacing a Strategy object at runtime.
*/
public function setStrategy(Strategy $strategy)
{
$this->strategy = $strategy;
}
/**
* The Context delegates some work to the Strategy object instead of
* implementing multiple versions of the algorithm on its own.
*/
public function doSomeBusinessLogic(): void
{
// ...
echo "Context: Sorting data using the strategy (not sure how it'll do it)\n";
$result = $this->strategy->doAlgorithm(["a", "b", "c", "d", "e"]);
echo implode(",", $result) . "\n";
// ...
}
}
/**
* The Strategy interface declares operations common to all supported versions
* of some algorithm.
*
* The Context uses this interface to call the algorithm defined by Concrete
* Strategies.
*/
interface Strategy
{
public function doAlgorithm(array $data): array;
}
/**
* Concrete Strategies implement the algorithm while following the base Strategy
* interface. The interface makes them interchangeable in the Context.
*/
class ConcreteStrategyA implements Strategy
{
public function doAlgorithm(array $data): array
{
sort($data);
return $data;
}
}
class ConcreteStrategyB implements Strategy
{
public function doAlgorithm(array $data): array
{
rsort($data);
return $data;
}
}
/**
* The client code picks a concrete strategy and passes it to the context. The
* client should be aware of the differences between strategies in order to make
* the right choice.
*/
$context = new Context(new ConcreteStrategyA());
echo "Client: Strategy is set to normal sorting.\n";
$context->doSomeBusinessLogic();
echo "\n";
echo "Client: Strategy is set to reverse sorting.\n";
$context->setStrategy(new ConcreteStrategyB());
$context->doSomeBusinessLogic();
** Output.txt: 执行结果
Client: Strategy is set to normal sorting.
Context: Sorting data using the strategy (not sure how it'll do it)
a,b,c,d,e
Client: Strategy is set to reverse sorting.
Context: Sorting data using the strategy (not sure how it'll do it)
