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

1 files changed, 31 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/module/attr_accessor_with_default.rb b/activesupport/lib/active_support/core_ext/module/attr_accessor_with_default.rb
new file mode 100644
index 0000000000..31f14be344
--- /dev/null
+++ b/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