On Sat, 07 Aug 2010 03:55:25 +0100, Etienne Kneuss <etie...@immomigsa.ch>
wrote:
Returning a ref is an additional constraint, meaning that it would
actually be covariance, and not contravariance. But yes, it makes
sense.
Yes, you are right. To put it another way: a subclass should be able to
* Relax the preconditions
* Strengthen the post-conditions
I actually noticed this shortly after sending the e-mail, but hoped no one
else would :p
Actually, after rereading what you said and the proposed diff, I'm not
sure it makes sense. It should _not_ be consistent with arguments.
A method subtype may relax the parent prototype by not requiring a
ref for an argument. This is fine and it's indeed contra-variant.
Again, my mistake. The if before was indeed about arguments...
However, the return value of a method subtype should be able to return a
ref even if the parent prototype doesnt. However, if the parent requires
a ref, the child should too. Which is covariant.
I'm confused, this was what exactly what I suggested.
The condition I suggested is this (proto is the parent, fe the child):
if (proto->common.return_reference && !fe->common.return_reference) {
return 0;
}
So it returns an error condition if the parent returns a reference and the
child doesn't.
It's the check on the arguments that's wrong in this sense. However, I
think invariance should be required here. The thing is, passing an
argument by reference is actually also a post-condition -- if we pass an
argument by reference, we're going to do something with it.
In fact, invariance is required for the non-"rest" part of the arguments:
if (fe->common.arg_info[i].pass_by_reference !=
proto->common.arg_info[i].pass_by_reference) {
Again, sorry for the confusion.
--
Gustavo Lopes
--
PHP Internals - PHP Runtime Development Mailing List
To unsubscribe, visit: http://www.php.net/unsub.php
