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

   1 class Module
   2   # Declare an attribute accessor with an initial default return value.
   3   #
   4   # To give attribute <tt>:age</tt> the initial value <tt>25</tt>:
   5   #
   6   #   class Person
   7   #     attr_accessor_with_default :age, 25
   8   #   end
   9   #
  10   #   some_person.age
  11   #   => 25
  12   #   some_person.age = 26
  13   #   some_person.age
  14   #   => 26
  15   #
  16   # To give attribute <tt>:element_name</tt> a dynamic default value, evaluated
  17   # in scope of self:
  18   #
  19   #   attr_accessor_with_default(:element_name) { name.underscore }
  20   #
  21   def attr_accessor_with_default(sym, default = nil, &block)
  22     raise 'Default value or block required' unless !default.nil? || block
  23     define_method(sym, block_given? ? block : Proc.new { default })
  24     module_eval(<<-EVAL, __FILE__, __LINE__)
  25       def #{sym}=(value)
  26         class << self; attr_reader :#{sym} end
  27         @#{sym} = value
  28       end
  29     EVAL
  30   end
  31 end