Add Module#attr_accessor_with_default to initialize value of attribute before setting it. Closes #6538. [Stuart Halloway, Marcel Molina Jr.]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5539 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Add Module#attr_accessor_with_default to initialize value of attribute before setting it. Closes #6538. [Stuart Halloway, Marcel Molina Jr.]
+
 * Hash#to_xml handles keys with the same name as Kernel methods.  #6613 [Catfish]
 
 * Added Time#end_of_day to get 23:59:59 of that day [DHH]

activesupport/lib/active_support/core_ext/module.rb

@@ -1,6 +1,7 @@
 require File.dirname(__FILE__) + '/module/inclusion'
 require File.dirname(__FILE__) + '/module/attribute_accessors'
 require File.dirname(__FILE__) + '/module/attr_internal'
+require File.dirname(__FILE__) + '/module/attr_accessor_with_default'
 require File.dirname(__FILE__) + '/module/delegation'
 require File.dirname(__FILE__) + '/module/introspection'
 require File.dirname(__FILE__) + '/module/loading'

activesupport/lib/active_support/core_ext/module/attr_accessor_with_default.rb

@@ -0,0 +1,31 @@
+class Module
+  # Declare an attribute accessor with an initial default return value.
+  #
+  # To give attribute <tt>:age</tt> the initial value <tt>25</tt>:
+  #  
+  #   class Person
+  #     attr_accessor_with_default :age, 25
+  #   end
+  #
+  #   some_person.age
+  #   => 25
+  #   some_person.age = 26
+  #   some_person.age
+  #   => 26
+  #
+  # To give attribute <tt>:element_name</tt> a dynamic default value, evaluated
+  # in scope of self:
+  #
+  #   attr_accessor_with_default(:element_name) { name.underscore } 
+  #
+  def attr_accessor_with_default(sym, default = nil, &block)
+    raise 'Default value or block required' unless default || block
+    define_method(sym, block_given? ? block : Proc.new { default })
+    module_eval(<<-EVAL, __FILE__, __LINE__)
+      def #{sym}=(value)
+        class << self; attr_reader :#{sym} end
+        @#{sym} = value
+      end
+    EVAL
+  end
+end

activesupport/test/core_ext/module/attr_accessor_with_default.rb

@@ -0,0 +1,30 @@
+require File.dirname(__FILE__) + '/../../abstract_unit'
+
+class AttrWithDefaultTest < Test::Unit::TestCase
+  def setup
+    @target = Class.new do
+      def helper
+        'helper'
+      end
+    end  
+    @instance = @target.new
+  end
+  
+  def test_default_arg
+    @target.attr_accessor_with_default :foo, :bar
+    assert_equal(:bar, @instance.foo)
+    @instance.foo = nil
+    assert_nil(@instance.foo)
+  end
+  
+  def test_default_proc
+    @target.attr_accessor_with_default(:foo) {helper.upcase}
+    assert_equal('HELPER', @instance.foo)
+    @instance.foo = nil
+    assert_nil(@instance.foo)
+  end
+  
+  def test_invalid_args
+    assert_raise(RuntimeError) {@target.attr_accessor_with_default :foo}
+  end
+end