introduce Enum

lib/enum.rb

@@ -0,0 +1,46 @@
+class Enum < SimpleDelegator
+  # Public: Initialize an enum.
+  #
+  # members - the array of enum members. May contain a hash of options:
+  #           :start   - the number of first enum member. Defaults to 1.
+  #
+  # Examples
+  #
+  #   FRUITS = Enum.new(:apple, :orange, :kiwi)
+  def initialize(*members)
+    super({})
+
+    options = members.extract_options!
+    start = options.fetch(:start) { 1 }
+
+    update Hash[members.zip(start..members.count + start)]
+  end
+
+  # Public: Access the number/value of member.
+  #
+  # ids_or_value - number or value of member.
+  #
+  # Returns value if number was provided, and number if value was provided.
+  def [](id_or_value)
+    fetch(id_or_value) { key(id_or_value) }
+  end
+
+  # Public: Check if supplied member is valid.
+  def valid?(member)
+    has_key?(member)
+  end
+
+  # Public: Create a subset of enum, only include specified keys.
+  def only(*keys)
+    dup.tap do |d|
+      d.__getobj__.keep_if { |k| keys.include?(k) }
+    end
+  end
+
+  # Public: Create a subset of enum, preserve all items but specified ones.
+  def except(*keys)
+    dup.tap do |d|
+      d.__getobj__.delete_if { |k| keys.include?(k) }
+    end
+  end
+end