Polymorphic Ruby SimpleDelegator

Question

SimpleDelegator有什麼替代方案來利用多態而不修改底層對象。

這是一個例子和SimpleDelegator沒有解決的問題。

目標是能夠用其他任何（yak_food）包裝原始對象（delicious_food），以便替換方法（delicious?）取決於底層的未替換方法。

class Food 
    def initialize(color) 
    @color = color 
    end 

    def delicious? 
    color == :red 
    end 

    def color 
    @color 
    end 
end 

class FoodTasteOverride < SimpleDelegator 
    def color 
    :green 
    end 
end 

delicious_food = Food.new(:red) 
yak_food = FoodTasteOverride.new delicious_food 

delicious_food.delicious? # true - expected 
yak_food.delicious? # expecting false, but is true since the color come from delicious_food 

什麼是將實際使用替代方法的替代方案？限制是你不能修改底層對象，它的類或者克隆。

約束意味着你不能做到這一點：

yak_food = delicious_food.clone 
def yak_food.color 
    :green 
end 

Answer 1

另一種方法是使用擴展擴展您的實例的方法。 （這是大多數DCI實現都在運行時延長使用行爲對象）

class Food 

    attr_reader :color 

    def initialize(color) 
    @color = color 
    end 

    def delicious? 
    self.color == :red 
    end 

end 

module FoodTasteOverride 
    def color 
    :green 
    end 
end 


normal_food = Food.new(:red) 
delicious_food = Food.new(:red) 
yak_food = normal_food.extend(FoodTasteOverride) 

puts delicious_food.delicious? # true - expected 
puts yak_food.delicious? #false because the color is now green.