:allow_nil option for delegate

+1: This seems like a good addition to delegate, and I like the simplicity of the implementation.

+1

1. Useful, and the patch is very simple.

If anything, I'd change the rdoc to say "If the object to which you delegate...".

(Um, that "1." in the comment above was supposed to be a "+1").

-1

I dislike silently hiding errors like that. Seems like just asking for trouble.

How is it hiding the error any more than:

def contact_name; contact && contact.name; end

It's intended as a shortcut for the case where not having a contact isn't an error. Remember you have to specify :allow_nil, this isn't going to be default behaviour.

I updated the patch, which no longer applied after the :prefix option was added.

@Josh, as Dave explained, this option is intended only for the cases where this is not an error but a legitimate situation, just to avoid that verbose and ugly definition.

I'd like some more attention brought on this ticket (i.e. BUMP), as I've recently found use cases for it abound.

I currently have the following simplified setup:

# A resident may or may not have a current residentship -- he
# could be a former resident.
class Resident < ActiveRecord::Base
  has_many :residentships

  delegate :room_number, :room, :to => :residentship

  def residentship
    residentships.only_current.first
  end
end

class Residentship < ActiveRecord::Base
  belongs_to :resident
  validates_presence_of :room_number, :moved_out_at
  named_scope :only_current, ...
  composed_of :room, :mapping => %w(room_number number)
end

class Room # value class, as there's a finite set of rooms
  def residentship
    Residentship.only_current.find_by_room_number(@number)
  end

  delegate :resident, :to => :residentships
end

I'd like Room#resident, Resident#room and Resident#room_number (as well as several more in my real app) to work properly for former residents, i.e. just return nil -- but with the current implementation of delegate, they raise an exception instead. Adding an :allow_nil option to delegate would greatly reduce the number of extra methods i need to have.

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