Question

Consider I have this following model definition, I want a particular property which should be constant from the moment it has been created

class A
  property :a1, String, :freeze => true
end

Is there something like this? or may be using callbacks ?

Answer 1

Try the following:

class YourModel
  property :a1, String

  def a1=(other)
    if a1 
      raise "A1 is allready bound to a value"
    end
    attribute_set(:a1, other.dup.freeze)
  end
end

The initializer internally delegates to normal attribute writers, so when you initialize the attribute via YourModel.new(:a1 => "Your value") you cannot change it with your_instance.a1 = "your value".. But when you create a fresh instance. instance = YourModel.new you can assign once instance.a1 = "Your Value".