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bin/gems/hashery-2.1.2/lib/hashery/association.rb

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+module Hashery
+
+  # TODO: Should associations be singleton?
+  #
+  # TODO: Is it really wise to keep a table of all associations?
+
+  # Association is a general binary association that allows one
+  # object to be associated with another. It has a variety of uses,
+  # such as linked-lists, simple ordered maps and mixed collections,
+  # among them.
+  #
+  # NOTE: This class is still fairly experimental. And it is not
+  # loaded along with the other Hashery libraries when using
+  # `require 'hashery'`. It must be required independently.
+  #
+  # Associations can be used to draw simple relationships.
+  #
+  #   :Apple >> :Fruit
+  #   :Apple >> :Red
+  #
+  #   :Apple.associations #=> [ :Fruit, :Red ]
+  #
+  # It can also be used for simple lists of ordered pairs.
+  #
+  #   c = [ :a >> 1, :b >> 2 ]
+  #   c.each { |k,v| puts "#{k} associated with #{v} }
+  #
+  # produces
+  #
+  #   a associated with 1
+  #   b associated with 2
+  #
+  # The method :>> is used to construct the association.
+  # It is a rarely used method so it is generally available.
+  # But you can't use it for any of the following classes
+  # becuase they use #>> for other things.
+  #
+  #   Bignum
+  #   Fixnum
+  #   Date
+  #   IPAddr
+  #   Process::Status
+  #
+  class Association
+    include Comparable
+
+    class << self
+      #
+      # Store association references.
+      #
+      # Returns `Hash` of all associaitons.
+      #
+      def reference
+        @reference ||= Hash.new{ |h,k,v| h[k]=[] }
+      end
+
+      #
+      # Shortcut for #new.
+      #
+      # index - The "index key" of the association.
+      # value - The "value" of the association.
+      #
+      # Returns `Association`.
+      #
+      def [](index, value)
+        new(index, value)
+      end
+
+      #def new(index, value)
+      #  lookup[[index, value]] ||= new(index, value)
+      #end
+
+      #def lookup
+      #  @lookup ||= {}
+      #end
+    end
+
+    #
+    # The "index key" of the association.
+    #
+    attr_accessor :index
+
+    #
+    # The "value" of the association.
+    #
+    attr_accessor :value
+
+    #
+    # Initialize new Association.
+    #
+    # index - The "index key" of the association.
+    # value - The "value" of the association.
+    #
+    def initialize(index, value=nil)
+      @index = index
+      @value = value
+
+      unless index.associations.include?(value)
+        index.associations << value
+      end
+    end
+
+    #
+    # Compare the values of two associations.
+    #
+    # TODO: Comparions with non-associations?
+    #
+    # assoc - The other `Association`.
+    #
+    # Returns [Integer] `1`, `0`, or `-1`.
+    #
+    def <=>(assoc)
+      return -1 if self.value < assoc.value
+      return  1 if self.value > assoc.value
+      return  0 if self.value == assoc.value
+    end
+
+    #
+    # Invert association, making the index the value and vice-versa.
+    #
+    # Returns [Array] with two-elements reversed.
+    #
+    def invert!
+      temp = @index
+      @index = @value
+      @value = temp
+    end
+
+    #
+    # Produce a string representation.
+    #
+    # Returns [String].
+    #
+    def to_s
+      return "#{index} >> #{value}"
+    end
+
+    #
+    # Produce a literal code string for creating an association.
+    #
+    # Returns [String].
+    #
+    def inspect
+      "#{index.inspect} >> #{value.inspect}"
+    end
+
+    #
+    # Convert to two-element associative array.
+    #
+    # Returns [Array] Two-element Array of index and value pair.
+    #
+    def to_ary
+      [index, value]
+    end
+
+    #
+    # Object extensions.
+    #
+    module Kernel
+
+      #
+      # Define an association for +self+.
+      #
+      # to - The value of the association.
+      #
+      # Returns [Association].
+      #
+      def >>(to)
+        Association.new(self, to)
+      end
+
+      #
+      # List of associations for this object.
+      #
+      # Returns an `Array` of `Associations`.
+      #
+      def associations
+        Association.reference[self]
+      end
+
+    end
+
+  end
+
+end
+
+class Object #:nodoc:
+  include Hashery::Association::Kernel
+end
+
+#--
+# Setup the >> method in classes that use it already.
+#
+# This is a bad idea b/c it can cause backward compability issues.
+#
+# class Bignum
+#   alias_method( :rshift, :>>) if method_defined?(:>>)
+#   remove_method :>>
+# end
+#
+# class Fixnum
+#   alias_method( :rshift, :>>) if method_defined?(:>>)
+#   remove_method :>>
+# end
+#
+# class Date
+#   alias_method( :months_later, :>>) if method_defined?(:>>)
+#   remove_method :>>
+# end
+#
+# class IPAddr
+#   alias_method( :rshift, :>>) if method_defined?(:>>)
+#   remove_method :>>
+# end
+#
+# class Process::Status
+#   alias_method( :rshift, :>>) if method_defined?(:>>)
+#   remove_method :>>
+# end
+#++
+
+# Copyright (c) 2005 Rubyworks, Thomas Sawyer