![Template Method](/images/patterns/cards/template-method-mini.png?id=9f200248d88026d8e79d0f3dae411ab4)
Template Method em Ruby
O Template Method é um padrão de projeto comportamental que permite definir o esqueleto de um algoritmo em uma classe base e permitir que as subclasses substituam as etapas sem alterar a estrutura geral do algoritmo.
Complexidade:
Popularidade:
Exemplos de uso: O padrão Template Method é bastante comum nos frameworks Ruby. Os desenvolvedores costumam usá-lo para fornecer aos usuários do framework um meio simples de estender a funcionalidade padrão usando herança.
Identificação: O Template Method pode ser reconhecido por métodos comportamentais que já possuem um comportamento “padrão” definido pela classe base.
Exemplo conceitual
Este exemplo ilustra a estrutura do padrão de projeto Template 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?
main.rb: Exemplo conceitual
# 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.
def template_method
base_operation1
required_operations1
base_operation2
hook1
required_operations2
base_operation3
hook2
end
# These operations already have implementations.
def base_operation1
puts 'AbstractClass says: I am doing the bulk of the work'
end
def base_operation2
puts 'AbstractClass says: But I let subclasses override some operations'
end
def base_operation3
puts 'AbstractClass says: But I am doing the bulk of the work anyway'
end
# These operations have to be implemented in subclasses.
def required_operations1
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
# @abstract
def required_operations2
raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
end
# 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.
def hook1; end
def hook2; end
end
# Concrete classes have to implement all abstract operations of the base class.
# They can also override some operations with a default implementation.
class ConcreteClass1 < AbstractClass
def required_operations1
puts 'ConcreteClass1 says: Implemented Operation1'
end
def required_operations2
puts 'ConcreteClass1 says: Implemented Operation2'
end
end
# Usually, concrete classes override only a fraction of base class' operations.
class ConcreteClass2 < AbstractClass
def required_operations1
puts 'ConcreteClass2 says: Implemented Operation1'
end
def required_operations2
puts 'ConcreteClass2 says: Implemented Operation2'
end
def hook1
puts 'ConcreteClass2 says: Overridden Hook1'
end
end
# 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.
def client_code(abstract_class)
# ...
abstract_class.template_method
# ...
end
puts 'Same client code can work with different subclasses:'
client_code(ConcreteClass1.new)
puts "\n"
puts 'Same client code can work with different subclasses:'
client_code(ConcreteClass2.new)
output.txt: Resultados da execução
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