method

attr_accessor_with_default

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What's this?

attr_accessor_with_default(sym, default = nil, &block) public

Declare an attribute accessor with an initial default return value.

To give attribute :age the initial value 25:

  class Person
    attr_accessor_with_default :age, 25
  end

  some_person.age
  => 25
  some_person.age = 26
  some_person.age
  => 26

To give attribute :element_name a dynamic default value, evaluated in scope of self:

  attr_accessor_with_default(:element_name) { name.underscore }

Show source

# File activesupport/lib/active_support/core_ext/module/attr_accessor_with_default.rb, line 21
  def attr_accessor_with_default(sym, default = nil, &block)
    raise 'Default value or block required' unless !default.nil? || block
    define_method(sym, block_given? ? block : Proc.new { default })
    module_eval("def \#{sym}=(value)                        # def age=(value)\nclass << self; attr_reader :\#{sym} end  #   class << self; attr_reader :age end\n@\#{sym} = value                         #   @age = value\nend                                       # end\n", __FILE__, __LINE__ + 1)
  end

September 13, 2011

1 thank

Some unexpected behaviour

When using Array as default value, it behaves more like cattr_accessor…

class A
 attr_accessor_with_default :b, []
end

x = A.new
x.b << 1

#puts x.b.inspect => [1]

y = A.new
y.b << 2

#puts y.b.inspect => [1, 2]

October 10, 2011 - (>= v3.1.0)

1 thank

Use Ruby instead!

E.g.

class TestClass < SomeSuperClass
  attr_accessor :sample_acc

  def initialize      
    @sample_acc = []
    super
  end
end

If nil is not a valid value for this accessor, then you can just define reader for it.

class TestClass
  attr_accessor :sample_acc

  def sample_acc
    @sample_acc ||= 98
  end
end

attr_accessor_with_default

Related methods

Some unexpected behaviour

Use Ruby instead!