Add private_alias_method

Author: Tim Perkins

README.md

@@ -57,6 +57,7 @@ class Bar
   private_attr_accessor :foo
   private_attr_reader :baz
   private_attr_writer :bat
+  private_alias_method :bar, :foo
 
   def initialize foo
     self.foo = foo

lib/private_attr.rb

@@ -32,4 +32,9 @@ def protected_attr_writer *attr
     attr_writer(*attr)
     protected(*attr.map { |a| "#{a}=" })
   end
+
+  def private_alias_method(new_name, old_name)
+    alias_method(new_name, old_name)
+    private(new_name)
+  end
 end

spec/private_attr_spec.rb

@@ -33,13 +33,24 @@ def write_writer value
   def write_writer_other other, value
     other.writer = value
   end
+
+  attr_reader :original
+
+  def call_aliased
+    aliased
+  end
+
+  def call_aliased_other other
+    other.aliased
+  end
 end
 
 class PrivateDummy < Dummy
   extend PrivateAttr
   private_attr_accessor :accessor
   private_attr_reader :reader
   private_attr_writer :writer
+  private_alias_method :aliased, :original
 end
 
 class ProtectedDummy < Dummy
@@ -147,6 +158,47 @@ class ProtectedDummy < Dummy
     end
   end
 
+  describe 'private_alias_method' do
+    let(:dummy_class) { PrivateDummy }
+
+    before { dummy.instance_variable_set '@original', old_value }
+
+    it 'allows alias to be called internally' do
+      dummy.call_aliased.must_equal old_value
+    end
+
+    it 'raises Error when alias is called externally' do
+      -> { dummy.call_aliased_other other }.must_raise NoMethodError
+    end
+
+    it 'allows the original method to be called externally' do
+      dummy.original.must_equal old_value
+    end
+
+    describe 'when the original method is overridden' do
+      let(:dummy_class) do
+        mod = Module.new do
+          def original
+            super.upcase
+          end
+        end
+        Class.new(PrivateDummy).include(mod)
+      end
+
+      it 'allows alias to be called internally' do
+        dummy.call_aliased.must_equal old_value
+      end
+
+      it 'raises Error when alias is called externally' do
+        -> { dummy.call_aliased_other other }.must_raise NoMethodError
+      end
+
+      it 'allows the overridden method to be called externally' do
+        dummy.original.must_equal old_value.upcase
+      end
+    end
+  end
+
   describe 'protected_attr_accessor' do
     let(:dummy_class) { ProtectedDummy }