Contents

=begin rdoc

= NilComparable

NilComparable does two things. First it make nil comparable, such that 
all things (except itself) are greater than it.

Secondly it provides a module called NilComparable to include into any
other class to allow it to compare itself to NilClass as the greater
of the two.

= Author(s)

* Paul Brannan
* Thomas Sawyer

=end

class NilClass
  include Comparable
  def <=>(x)
    x.nil? ? 0 : -1
  end
  alias_method( :cmp, :<=> )
end

# # Calling this method for a given class allows instances
# # of a class to be compared to nil using <=>.
# # Adapted from code by Paul Brannan (Ruby License)
# # NOTE: THIS SHOULD BE A CLASS INCLUDING MODULE, I THINK.
# def nil_comparable(klass=self)
#   klass.class_eval %{
#     if method_defined?( :<=> )
#       alias_method :compare_without_nil, :<=>
#     else
#       def compare_without_nil( other )
#         raise TypeError, "Cannot compare \#{self.inspect} to \#{other.inspect}"
#       end
#     end
#     def <=>( other )
#       return 1 if other.nil?
#       compare_without_nil( other )
#     end
#   }
# end

module NilComparable

  def self.included( mod )
    mod.class_eval %{
      if method_defined?( :<=> )
        alias_method :compare_without_nil, :<=>
      else
        def compare_without_nil( other )
          raise TypeError, "Cannot compare \#{self.inspect} to \#{other.inspect}"
        end
      end
      def <=>( other )
        return 1 if other.nil?
        compare_without_nil( other )
      end
    }
  end

end

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
carats-0.3.0	lib/carat/nil-comparable.rb