Refactor code common to Twitter::Base#attr_reader and object_attr_reader

lib/twitter/base.rb

@@ -12,57 +12,68 @@ class Base
 
     # Define methods that retrieve the value from an initialized instance variable Hash, using the attribute as a key
     #
-    # @param attrs [Array, Set, Symbol]
+    # @param attrs [Array, Symbol]
     def self.attr_reader(*attrs)
-      mod = Module.new do
-        attrs.each do |attribute|
-          define_method attribute do
-            @attrs[attribute.to_sym]
-          end
-          define_method "#{attribute}?" do
-            !!@attrs[attribute.to_sym]
-          end
-        end
+      attrs.each do |attr|
+        define_attribute_method(attr)
+        define_predicate_method(attr)
       end
-      const_set(:Attributes, mod)
-      include mod
     end
 
-    # Construct an object from a response hash
+    # Create a new object (or NullObject) from attributes
     #
-    # @param response [Hash]
-    # @return [Twitter::Base]
-    def self.from_response(response={})
-      new(response[:body])
+    # @param klass [Symbol]
+    # @param key1 [Symbol]
+    # @param key2 [Symbol]
+    def self.object_attr_reader(klass, key1, key2=nil)
+      define_attribute_method(key1, klass, key2)
+      define_predicate_method(key1)
     end
 
-    # Create a new object (or NullObject) from attributes
+    # Dynamically define a method for an attribute
     #
-    # @param klass [Class]
     # @param key1 [Symbol]
+    # @param klass [Symbol]
     # @param key2 [Symbol]
-    def self.object_attr_reader(klass, key1, key2=nil)
-      define_method key1 do
-        ivar = :"@#{key1}"
-        return instance_variable_get(ivar) if instance_variable_defined?(ivar)
-        object = if @attrs[key1]
-          if key2.nil?
-            Twitter.const_get(klass).new(@attrs[key1])
+    def self.define_attribute_method(key1, klass=nil, key2=nil)
+      define_method(key1) do
+        memoize(key1) do
+          if klass.nil?
+            @attrs[key1]
           else
-            attrs = @attrs.dup
-            value = attrs.delete(key1)
-            Twitter.const_get(klass).new(value.update(key2 => attrs))
+            if @attrs[key1]
+              if key2.nil?
+                Twitter.const_get(klass).new(@attrs[key1])
+              else
+                attrs = @attrs.dup
+                value = attrs.delete(key1)
+                Twitter.const_get(klass).new(value.update(key2 => attrs))
+              end
+            else
+              Twitter::NullObject.new
+            end
           end
-        else
-          Twitter::NullObject.new
         end
-        instance_variable_set(ivar, object)
       end
-      define_method "#{key1}?" do
-        !!self.send(key1)
+    end
+
+    # Dynamically define a predicate method for an attribute
+    #
+    # @param key [Symbol]
+    def self.define_predicate_method(key)
+      define_method(:"#{key}?") do
+        !!send(key)
       end
     end
 
+    # Construct an object from a response hash
+    #
+    # @param response [Hash]
+    # @return [Twitter::Base]
+    def self.from_response(response={})
+      new(response[:body])
+    end
+
     # Initializes a new object
     #
     # @param attrs [Hash]
@@ -75,11 +86,18 @@ def initialize(attrs={})
     #
     # @param method [String, Symbol] Message to send to the object
     def [](method)
-      send(method.to_sym)
+      send(method)
     rescue NoMethodError
       nil
     end
 
+    def memoize(key, &block)
+      ivar = :"@#{key}"
+      return instance_variable_get(ivar) if instance_variable_defined?(ivar)
+      result = block.call
+      instance_variable_set(ivar, result)
+    end
+
   private
 
     # @param attr [Symbol]