Em Sun, 18 Sep 2011 20:06:31 +0100, Stas Malyshev <smalys...@sugarcrm.com>
escreveu:
On 9/18/11 11:23 AM, Nikita Popov wrote:
to tell you: I need this and that method accepting these and these
arguments to work correctly. If the signature isn't enforced, this
doesn't make sense anymore. You could just as well drop the signature
from abstract method definitions, as it's pointless then.
No it is not. The signature tells "this method would accept certain
arguments". If you call it with these arguments, it would work. However,
there's no promise to never extend the cases where it works - it goes
contrary to the whole point of OOP to say "I will never loosen
preconditions on my methods".
While this is true, we should be a bit pragmatic here.
If the subclass method specifies less parameters, it is very likely a
mistake. It's not usual (certainly it's not more frequent than a mistake
being the case) for arguments to be simply intentionally ignored. In fact,
I don't know of any popular language that implements this type of
contravariance. Plus, consider the case in which the superclass takes an
argument by reference:
function increment(&$foo) { $foo = $foo + 1; }
It is obvious that in this case a subclass override that takes no
arguments cannot possibly satisfy the contract of the original method.
That is to say, by ref arguments are also used for postconditions.
That said, I think the only rules worth implementing are:
* Allow arguments with a supertype. For instance, this should give no
warning:
<?php
class A {}
class B extends A {}
class C { function g(B $b) {} }
class D extends C { function g(A $a) { } }
* Allow extra parameters with a default value (implemented):
<?php
class C { function g($a) {} }
class D extends C { function g($a,$b=true) { } }
--
Gustavo Lopes
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