83 lines
1.5 KiB
Ruby
83 lines
1.5 KiB
Ruby
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# Liskov’s principle tends to be the most difficult to understand. The principle
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# states that you should be able to replace any instances of a parent class
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# with an instance of one of its children without creating any unexpected or
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# incorrect behaviors.
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class Rectangle
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def initialize(height, width)
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@height = height
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@width = width
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end
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def set_height(height)
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@height = height
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end
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def set_width(width)
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@width = width
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end
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def square
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@width * @height
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end
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end
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# Solution
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# LSP says is if we know the interface of Rectangle, We need to be able to guess
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# the interface of subtype class Square
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# Square.new(3).square => 9
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class Square < Rectangle
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def initialize(side)
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super(side, side)
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end
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def set_height(height)
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super(height)
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@width = height
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end
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def set_width(width)
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super(width)
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@height = width
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end
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end
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# Another common instance of a Liskov violation is raising an exception for an
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# overridden method in a child class. It’s also not uncommon to see methods
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# overridden with modified method signatures causing branching on type in
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# classes that depend on objects of the parent’s type. All of these either
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# lead to unstable code or unnecessary and ugly branching.
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class Animal
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def walk
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'walking_as_animal'
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end
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end
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class Cat < Animal
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def run
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'run_as_cat'
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end
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end
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# Solution
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class Animal
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def walk
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'walking_as_animal'
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end
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def run
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raise NotImplementedError
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end
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end
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class Cat < Animal
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def run
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'run_as_cat'
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end
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end
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