Merge pull request #10848 from 907th/add_block_to_cattr_reader

Fix #10847: allow to pass a block to `cattr_reader`.

activesupport/CHANGELOG.md

+*   Unify `cattr_*` interface: allow to pass a block to `cattr_reader`.
+
+    Example:
+
+        class A
+          cattr_reader(:defr) { 'default_reader_value' }
+        end
+        A.defr # => 'default_reader_value'
+
+    *Alexey Chernenkov*
+
 *   Improved compatibility with the stdlib JSON gem.
 
     Previously, calling `::JSON.{generate,dump}` sometimes causes unexpected

activesupport/lib/active_support/core_ext/class/attribute_accessors.rb

@@ -29,6 +29,16 @@ class Class
   #   end
   #
   #   Person.new.hair_colors # => NoMethodError
+  #
+  # Also, you can pass a block to set up the attribute with a default value.
+  #
+  #   class Person
+  #     cattr_reader :hair_colors do
+  #       [:brown, :black, :blonde, :red]
+  #     end
+  #   end
+  #
+  #   Person.hair_colors # => [:brown, :black, :blonde, :red]
   def cattr_reader(*syms)
     options = syms.extract_options!
     syms.each do |sym|
@@ -50,6 +60,7 @@ def #{sym}
           end
         EOS
       end
+      class_variable_set("@@#{sym}", yield) if block_given?
     end
   end
 

activesupport/test/core_ext/class/attribute_accessor_test.rb

@@ -8,6 +8,9 @@ def setup
       cattr_accessor :bar,  :instance_writer   => false
       cattr_reader   :shaq, :instance_reader   => false
       cattr_accessor :camp, :instance_accessor => false
+      cattr_accessor(:defa) { 'default_accessor_value' }
+      cattr_reader(:defr) { 'default_reader_value' }
+      cattr_writer(:defw) { 'default_writer_value' }
     end
     @object = @class.new
   end
@@ -58,4 +61,10 @@ def test_should_raise_name_error_if_attribute_name_is_invalid
     end
     assert_equal "invalid class attribute name: 1nvalid", exception.message
   end
+
+  def test_should_use_default_value_if_block_passed
+    assert_equal 'default_accessor_value', @class.defa
+    assert_equal 'default_reader_value', @class.defr
+    assert_equal 'default_writer_value', @class.class_variable_get('@@defw')
+  end
 end

guides/source/active_support_core_extensions.md

@@ -1093,6 +1093,15 @@ end
 
 we can access `field_error_proc` in views.
 
+Also, you can pass a block to `cattr_*` to set up the attribute with a default value:
+
+```ruby
+class MysqlAdapter < AbstractAdapter
+  # Generates class methods to access @@emulate_booleans with default value of true.
+  cattr_accessor(:emulate_booleans) { true }
+end
+```
+
 The generation of the reader instance method can be prevented by setting `:instance_reader` to `false` and the generation of the writer instance method can be prevented by setting `:instance_writer` to `false`. Generation of both methods can be prevented by setting `:instance_accessor` to `false`. In all cases, the value must be exactly `false` and not any false value.
 
 ```ruby