dup strings on return so that in place modifications do not break any…

…thing. I am looking at you "compute_table_name"

activemodel/lib/active_model/attribute_methods.rb

@@ -109,7 +109,7 @@ def define_attr_method(name, value=nil, &block)
           # use eval instead of a block to work around a memory leak in dev
           # mode in fcgi
           value = value.nil? ? 'nil' : value.to_s
-          sing.send(:define_method, name) { value }
+          sing.send(:define_method, name) { value.dup }
         end
       end
 

activemodel/test/cases/attribute_methods_test.rb

@@ -9,6 +9,10 @@ class << self
     define_method(:bar) do
       'original bar'
     end
+
+    define_method(:zomg) do
+      'original zomg'
+    end
   end
 
   def attributes
@@ -98,6 +102,13 @@ class AttributeMethodsTest < ActiveModel::TestCase
     assert_equal "value of foo bar", ModelWithAttributesWithSpaces.new.send(:'foo bar')
   end
 
+  def test_defined_methods_always_return_duped_string
+    ModelWithAttributes.define_attr_method(:zomg, 'lol')
+    assert_equal 'lol', ModelWithAttributes.zomg
+    ModelWithAttributes.zomg << 'bbq'
+    assert_equal 'lol', ModelWithAttributes.zomg
+  end
+
   test '#define_attr_method generates attribute method' do
     ModelWithAttributes.define_attr_method(:bar, 'bar')