Factory Method em TypeScript
O Factory method é um padrão de projeto criacional, que resolve o problema de criar objetos de produtos sem especificar suas classes concretas.
O Factory Method define um método, que deve ser usado para criar objetos em vez da chamada direta ao construtor (operador new). As subclasses podem substituir esse método para alterar a classe de objetos que serão criados.
Se você não conseguir descobrir a diferença entre os padrões Factory, Factory Method e Abstract Factory, leia nossa Comparação Factory.
Complexidade:
Popularidade:
Exemplos de uso: O padrão Factory Method é amplamente utilizado no código TypeScript. É muito útil quando você precisa fornecer um alto nível de flexibilidade para seu código.
Identificação: Os métodos fábrica podem ser reconhecidos por métodos de criação, que criam objetos de classes concretas, mas os retornam como objetos de tipo ou interface abstrata.
Exemplo conceitual
Este exemplo ilustra a estrutura do padrão de projeto Factory Method. Ele se concentra em responder a estas perguntas:
- De quais classes ele consiste?
- Quais papéis essas classes desempenham?
- De que maneira os elementos do padrão estão relacionados?
index.ts: Exemplo conceitual
/**
* The Creator class declares the factory method that is supposed to return an
* object of a Product class. The Creator's subclasses usually provide the
* implementation of this method.
*/
abstract class Creator {
/**
* Note that the Creator may also provide some default implementation of the
* factory method.
*/
public abstract factoryMethod(): Product;
/**
* Also note that, despite its name, the Creator's primary responsibility is
* not creating products. Usually, it contains some core business logic that
* relies on Product objects, returned by the factory method. Subclasses can
* indirectly change that business logic by overriding the factory method
* and returning a different type of product from it.
*/
public someOperation(): string {
// Call the factory method to create a Product object.
const product = this.factoryMethod();
// Now, use the product.
return `Creator: The same creator's code has just worked with ${product.operation()}`;
}
}
/**
* Concrete Creators override the factory method in order to change the
* resulting product's type.
*/
class ConcreteCreator1 extends Creator {
/**
* Note that the signature of the method still uses the abstract product
* type, even though the concrete product is actually returned from the
* method. This way the Creator can stay independent of concrete product
* classes.
*/
public factoryMethod(): Product {
return new ConcreteProduct1();
}
}
class ConcreteCreator2 extends Creator {
public factoryMethod(): Product {
return new ConcreteProduct2();
}
}
/**
* The Product interface declares the operations that all concrete products must
* implement.
*/
interface Product {
operation(): string;
}
/**
* Concrete Products provide various implementations of the Product interface.
*/
class ConcreteProduct1 implements Product {
public operation(): string {
return '{Result of the ConcreteProduct1}';
}
}
class ConcreteProduct2 implements Product {
public operation(): string {
return '{Result of the ConcreteProduct2}';
}
}
/**
* The client code works with an instance of a concrete creator, albeit through
* its base interface. As long as the client keeps working with the creator via
* the base interface, you can pass it any creator's subclass.
*/
function clientCode(creator: Creator) {
// ...
console.log('Client: I\'m not aware of the creator\'s class, but it still works.');
console.log(creator.someOperation());
// ...
}
/**
* The Application picks a creator's type depending on the configuration or
* environment.
*/
console.log('App: Launched with the ConcreteCreator1.');
clientCode(new ConcreteCreator1());
console.log('');
console.log('App: Launched with the ConcreteCreator2.');
clientCode(new ConcreteCreator2());
Output.txt: Resultados da execução
App: Launched with the ConcreteCreator1.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct1}
App: Launched with the ConcreteCreator2.
Client: I'm not aware of the creator's class, but it still works.
Creator: The same creator's code has just worked with {Result of the ConcreteProduct2}
