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PHP 模板方法模式讲解和代码示例

模版方法是一种行为设计模式， 它在基类中定义了一个算法的框架， 允许子类在不修改结构的情况下重写算法的特定步骤。

** 进一步了解模板方法模式 **

复杂度：******

流行度：******

使用示例： 模版方法模式在 PHP 框架中很常见。 该模式简化了通过类继承对默认框架行为进行扩展时的工作。

识别方法： 模版方法可以通过行为方法来识别， 该方法已有一个在基类中定义的 “默认” 行为。

概念示例真实世界示例

概念示例

本例说明了模版方法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\TemplateMethod\Conceptual;

/**
 * The Abstract Class defines a template method that contains a skeleton of some
 * algorithm, composed of calls to (usually) abstract primitive operations.
 *
 * Concrete subclasses should implement these operations, but leave the template
 * method itself intact.
 */
abstract class AbstractClass
{
    /**
     * The template method defines the skeleton of an algorithm.
     */
    final public function templateMethod(): void
    {
        $this->baseOperation1();
        $this->requiredOperations1();
        $this->baseOperation2();
        $this->hook1();
        $this->requiredOperation2();
        $this->baseOperation3();
        $this->hook2();
    }

    /**
     * These operations already have implementations.
     */
    protected function baseOperation1(): void
    {
        echo "AbstractClass says: I am doing the bulk of the work\n";
    }

    protected function baseOperation2(): void
    {
        echo "AbstractClass says: But I let subclasses override some operations\n";
    }

    protected function baseOperation3(): void
    {
        echo "AbstractClass says: But I am doing the bulk of the work anyway\n";
    }

    /**
     * These operations have to be implemented in subclasses.
     */
    abstract protected function requiredOperations1(): void;

    abstract protected function requiredOperation2(): void;

    /**
     * These are "hooks." Subclasses may override them, but it's not mandatory
     * since the hooks already have default (but empty) implementation. Hooks
     * provide additional extension points in some crucial places of the
     * algorithm.
     */
    protected function hook1(): void { }

    protected function hook2(): void { }
}

/**
 * Concrete classes have to implement all abstract operations of the base class.
 * They can also override some operations with a default implementation.
 */
class ConcreteClass1 extends AbstractClass
{
    protected function requiredOperations1(): void
    {
        echo "ConcreteClass1 says: Implemented Operation1\n";
    }

    protected function requiredOperation2(): void
    {
        echo "ConcreteClass1 says: Implemented Operation2\n";
    }
}

/**
 * Usually, concrete classes override only a fraction of base class' operations.
 */
class ConcreteClass2 extends AbstractClass
{
    protected function requiredOperations1(): void
    {
        echo "ConcreteClass2 says: Implemented Operation1\n";
    }

    protected function requiredOperation2(): void
    {
        echo "ConcreteClass2 says: Implemented Operation2\n";
    }

    protected function hook1(): void
    {
        echo "ConcreteClass2 says: Overridden Hook1\n";
    }
}

/**
 * The client code calls the template method to execute the algorithm. Client
 * code does not have to know the concrete class of an object it works with, as
 * long as it works with objects through the interface of their base class.
 */
function clientCode(AbstractClass $class)
{
    // ...
    $class->templateMethod();
    // ...
}

echo "Same client code can work with different subclasses:\n";
clientCode(new ConcreteClass1());
echo "\n";

echo "Same client code can work with different subclasses:\n";
clientCode(new ConcreteClass2());

** Output.txt:  执行结果

Same client code can work with different subclasses:
AbstractClass says: I am doing bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses to override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing bulk of the work anyway

Same client code can work with different subclasses:
AbstractClass says: I am doing bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses to override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing bulk of the work anyway