On Thu, 30 Sep 2010 16:25:28 +0100, Adam Harvey <ahar...@php.net> wrote:
The initial version of the patch actually did just that: it simply
modified zend_std_compare_objects. That's pretty much the cleanest way
you could do it. :)
(...) Additionally, there
are already semantics built into compare_function to handle
object/non-object comparisons, although they're of very limited use in
practice.
The specific use case I had in mind was allowing comparisons of
objects representing monetary amounts against numeric values (since
that was a particular itch I had a couple of years ago), but I'm sure
there would be others.
It's true that the engine already allows comparison of objects with
scalars, but that can only happen after a cast. At least you now have the
guarantee that if you compare a scalar x of type u with an object y and
they're equal, then x === (u) y is also true*.
With your patch, you could make $obj == "jjj" be true and (string) $obj
yield a completely different thing. Obviously you wouldn't do this on
purpose, my point is that this could lead to a hard to debug problem.
This is what makes me very reluctant to support this more general approach
of allowing scalar-object comparisons.
* (maybe there's some edge case where this wouldn't happen because the
engine is inconsistent with its preferences towards get, cast_object and
__toString, but my point stands)
In terms of the specific question as to whether equality is symmetric:
certainly it should be, but we would have no way of enforcing it,
obviously. Java doesn't either, though: there's simply a note in the
documentation saying that implementations should be symmetric.
Obviously it must be the programmer's responsibility to write a compare()
function that is symmetric (and in general, establish a total order).
My point about about symmetry was another: you know have potentially
different code running in these two cases:
$a == $b
$b == $a
The current implementation is "symmetric" in the sense the compare_objects
handler is called only if both objects have the same handler (only the
arguments are exchanged).
--
Gustavo Lopes
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