C++ 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。
复杂度：
流行度：
使用示例： 模版方法模式在 C++ 框架中很常见。 开发者通常使用它来向框架用户提供通过继承实现的、 对标准功能进行扩展的简单方式。
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
本例说明了模板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？
main.cc: 概念示例
/** * 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. */ class AbstractClass { /** * The template method defines the skeleton of an algorithm. */ public: void TemplateMethod() const { this->BaseOperation1(); this->RequiredOperations1(); this->BaseOperation2(); this->Hook1(); this->RequiredOperation2(); this->BaseOperation3(); this->Hook2(); } /** * These operations already have implementations. */ protected: void BaseOperation1() const { std::cout << "AbstractClass says: I am doing the bulk of the work\n"; } void BaseOperation2() const { std::cout << "AbstractClass says: But I let subclasses override some operations\n"; } void BaseOperation3() const { std::cout << "AbstractClass says: But I am doing the bulk of the work anyway\n"; } /** * These operations have to be implemented in subclasses. */ virtual void RequiredOperations1() const = 0; virtual void RequiredOperation2() const = 0; /** * 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. */ virtual void Hook1() const {} virtual void Hook2() const {} }; /** * Concrete classes have to implement all abstract operations of the base class. * They can also override some operations with a default implementation. */ class ConcreteClass1 : public AbstractClass { protected: void RequiredOperations1() const override { std::cout << "ConcreteClass1 says: Implemented Operation1\n"; } void RequiredOperation2() const override { std::cout << "ConcreteClass1 says: Implemented Operation2\n"; } }; /** * Usually, concrete classes override only a fraction of base class' operations. */ class ConcreteClass2 : public AbstractClass { protected: void RequiredOperations1() const override { std::cout << "ConcreteClass2 says: Implemented Operation1\n"; } void RequiredOperation2() const override { std::cout << "ConcreteClass2 says: Implemented Operation2\n"; } void Hook1() const override { std::cout << "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. */ void ClientCode(AbstractClass *class_) { // ... class_->TemplateMethod(); // ... } int main() { std::cout << "Same client code can work with different subclasses:\n"; ConcreteClass1 *concreteClass1 = new ConcreteClass1; ClientCode(concreteClass1); std::cout << "\n"; std::cout << "Same client code can work with different subclasses:\n"; ConcreteClass2 *concreteClass2 = new ConcreteClass2; ClientCode(concreteClass2); delete concreteClass1; delete concreteClass2; return 0; } Output.txt: 执行结果
Same client code can work with different subclasses: AbstractClass says: I am doing the bulk of the work ConcreteClass1 says: Implemented Operation1 AbstractClass says: But I let subclasses override some operations ConcreteClass1 says: Implemented Operation2 AbstractClass says: But I am doing the bulk of the work anyway Same client code can work with different subclasses: AbstractClass says: I am doing the bulk of the work ConcreteClass2 says: Implemented Operation1 AbstractClass says: But I let subclasses override some operations ConcreteClass2 says: Overridden Hook1 ConcreteClass2 says: Implemented Operation2 AbstractClass says: But I am doing the bulk of the work anyway 
