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Message-ID: <000901c63322$20b5d550$5c8be5a9@ohr.berkeley.edu>
Reply-To: "Sara Golemon" <saramg@berkeley.edu>
To: "Zeev Suraski" <zeev@zend.com>
Cc: <internals@lists.php.net>,
	"Andi Gutmans" <andi@zend.com>
References: <002201c6331d$a79473b0$58d01a44@stumpy> <7.0.1.0.2.20060216192615.099c9598@zend.com>
Date: Thu, 16 Feb 2006 09:55:09 -0800
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Subject: Re: Minor engine patch to facilitate PECL/operator
From: saramg@berkeley.edu ("Sara Golemon")

> >Enter PECL/operator, which tries to implement operator overloading
> >for objects (and does a decent job at that).  In the interrest of
> >ease of use and consistency, every overloaded binary operator is
> >[meant to be] left associative.  This is, in the expression   expr1
> >op expr2   expr1 gets to decide how it will combine-with/compare-to
expr2.
> >
> What does it mean that it gets to decide?  If it's left associative,
> then it's evaluated from left to right, no?
>
Yes, and that's the problem.   $a > $b *isn't* read by the current parser as
$a > $b, it's read as $b < $a.

For all normal PHP comparisons, the distinction is unimportant...    4 < 2
and 2 > 4 will both evaluate to false after all.

However, the way object operator overloading is being done is: If the first
operand is an object implementing an overload method for this op, dispatch
to that method rather than using the tranditional comparison function.  e.g.
$a < $b    turns into  $a->__is_smaller($b).

Now say you've got that expression the other way around:   $a > $b.   What
you'd expect is that if $a is an object, it'll try to call
$a->__is_greater($b).  What you get is an automatic reversal of the
expression by the engine:  $b < $a, which turns into: "If $b is an object,
dispatch to $b->__is_smaller($a);"   which is not the same thing.

-Sara