From: Yukihiro Matsumoto <matz@...>
Date: 2005-07-07T08:42:37+09:00
Subject: Re: Inheriting Array and slice() behaviour

Hi,

In message "Re: Inheriting Array and slice() behaviour"
    on Thu, 7 Jul 2005 07:54:17 +0900, William Morgan <wmorgan-ruby-talk@masanjin.net> writes:

|> Why?  I'd expect them to return instances of the class of the
|> receiver, as Daniel does in [ruby-talk:147323], since they are ripped
|> part of the receiver.
|
|But #+ returns an Array. Is that consistent?

The result from + method is not a sub-array.  Where X = A + B,
the possible choices of the class of X are:

  (a) assured common ancestor, i.e. Array
  (b) lowest common ancestor of A and B
  (c) class of A if A and B are instances of same class, Array otherwise

Currently (a) is my decision.  (b) is too expensive, I guess.  (c)
might be a good choice, but I'm not sure whether it's more useful than
the current one.

|Like the OP, I think it's weird and special-cased to have #slice
|magically return something with the receiver's class. Especially since
|the return value is going to be broken (not initialized) except in
|trivial cases.

What if it can be initialized properly?

							matz.