diff options
Diffstat (limited to 'activesupport/lib/active_support/core_ext/class/attribute.rb')
-rw-r--r-- | activesupport/lib/active_support/core_ext/class/attribute.rb | 30 |
1 files changed, 26 insertions, 4 deletions
diff --git a/activesupport/lib/active_support/core_ext/class/attribute.rb b/activesupport/lib/active_support/core_ext/class/attribute.rb index 576366e496..bfa57fe1f7 100644 --- a/activesupport/lib/active_support/core_ext/class/attribute.rb +++ b/activesupport/lib/active_support/core_ext/class/attribute.rb @@ -2,8 +2,8 @@ require 'active_support/core_ext/kernel/singleton_class' require 'active_support/core_ext/module/remove_method' class Class - # Declare a class-level attribute whose value is inheritable and - # overwritable by subclasses: + # Declare a class-level attribute whose value is inheritable by subclasses. + # Subclasses can change their own value and it will not impact parent class. # # class Base # class_attribute :setting @@ -18,12 +18,34 @@ class Class # Subclass.setting # => false # Base.setting # => true # + # In the above case as long as Subclass does not assign a value to setting + # by performing <tt>Subclass.setting = _something_ </tt>, <tt>Subclass.setting</tt> + # would read value assigned to parent class. Once Subclass assigns a value then + # the value assigned by Subclass would be returned. + # # This matches normal Ruby method inheritance: think of writing an attribute - # on a subclass as overriding the reader method. + # on a subclass as overriding the reader method. However, you need to be aware + # when using +class_attribute+ with mutable structures as +Array+ or +Hash+. + # In such cases, you don't want to do changes in places but use setters: + # + # Base.setting = [] + # Base.setting #=> [] + # Subclass.setting #=> [] + # + # # Appending in child changes both parent and child because it is the same object: + # Subclass.setting << :foo + # Base.setting #=> [:foo] + # Subclass.setting #=> [:foo] + # + # # Use setters to not propagate changes: + # Base.setting = [] + # Subclass.setting += [:foo] + # Base.setting #=> [] + # Subclass.setting #=> [:foo] # # For convenience, a query method is defined as well: # - # Subclass.setting? # => false + # Subclass.setting? # => false # # Instances may overwrite the class value in the same way: # |