Template Method en C++
Template Method es un patrón de diseño de comportamiento que te permite definir el esqueleto de un algoritmo en una clase base y permite a las subclases sobrescribir los pasos sin cambiar la estructura general del algoritmo.
Complejidad:
Popularidad:
Ejemplos de uso: El patrón Template Method es muy común en los frameworks C++. Los desarrolladores lo utilizan a menudo para proporcionar a los usuarios de frameworks medios sencillos para extender la funcionalidad estándar utilizando la herencia.
Identificación: El patrón Template Method se puede reconocer por los métodos de comportamiento que ya tienen un comportamiento “por defecto” definido por la clase base.
Ejemplo conceptual
Este ejemplo ilustra la estructura del patrón de diseño Template Method. Se centra en responder las siguientes preguntas:
- ¿De qué clases se compone?
- ¿Qué papeles juegan esas clases?
- ¿De qué forma se relacionan los elementos del patrón?
main.cc: Ejemplo 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.
*/
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: Resultado de la ejecución
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
