Template Method Pattern

You want to build a program to teach your children to know animals. You write class animal like that:

class Animal
  def initalize(name, age, species)
    @name = name
    @age = age
    @species = species
  end

  def say
    if(@species == "dog")
      puts "Gau...gau..gau..."
    end
    if(@species == "cat")
      puts "meo...meo...meo"
    end
  end
end

After that, you want to add more infomation about animals in your program. It’s a nightmare if you want to add more and more species in your old code.

Luckily, you can use template method patter to do it simply, easily. Like that

class  Animal
  def initialize(name, age)
    @name = name
    @age = age
  end

  def say
    raise 'Called say method in subclass'
  end
end

class Dog < Animal
  def say
    puts "Gau gau gau"
  end
end

class Cat < Animal
  def say
    puts "meo ... meo ...."
  end
end

At now, you can test it by

dog = Dog.new("some name", 2)
dog.say

Your result will be "Gau gau gau".

Congratulation! You learnt a pattern in 23 patterns of GoF. It is Template Method Pattern.