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lib/core/facets/comparable/op_get.rb

 

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module Comparable

 

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  # Automatically generate comparitive definitions based on

 

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  # attribute fields.

 

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  #

 

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  #   include Comparable[:a, :b]

 

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  #

 

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  # is equivalent to including a module containing:

 

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  #

 

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  #   def <=>(other)

 

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  #     cmp = self.a <=> other.a; return cmp unless cmp == 0

 

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  #     cmp = self.b <=> other.b; return cmp unless cmp == 0

 

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  #     0

 

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  #   end

 

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  #

 

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  def self.[](*accessors)

 

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    Module.new do

 

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      include Comparable

 

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      define_method(:comparability){ accessors }

 

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      define_method(:<=>) do |other|

 

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        comparability.each do |a|

 

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          cmp = (send(a) <=> other.send(a))

 

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          break cmp unless cmp == 0

 

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        end

 

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      end

 

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    end

 

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  end

 

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end

 

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# Would it be nice if we could define comparability for all objects?

 

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# Then Comparable[] method would not be needed. Just:

 

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#

 

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#   module Comparable

 

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#

 

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#    def <=>(other)

 

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#      comparability.each do |field|

 

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#        cmp = send(field) <=> other.send(field); return cmp unless cmp == 0

 

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#      end

 

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#    end

 

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#

 

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#  end

 

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#

 

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# But I fear it might break other code.

 

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