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Date: Sun, 9 Jun 2013 16:15:19 +0200
Message-ID: <CAF+90c_wSHUZvDFKrK2KHzyDCAPkKNCXcUwdnfEK2qt+a+WKLA@mail.gmail.com>
To: Zeev Suraski <zeev@zend.com>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=e89a8ff1c02a3b580504deb94bd4
Subject: Re: [PHP-DEV] [RFC] Internal operator overloading and GMP improvements
From: nikita.ppv@gmail.com (Nikita Popov)

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On Sun, Jun 9, 2013 at 3:37 PM, Zeev Suraski <zeev@zend.com> wrote:

> What I meant by cumulativity in that context is really commutativity J
> Fixed (and also added transitivity).
>
>
>
> In other words, operands that are commutative in PHP (like addition,
> multiplication, etc.) =96 one should not overload for domains where they=
=92re
> not commutative.
>
>
>
> Zeev
>

Why? For example matrix multiplication is not commutative, but I would
still consider writing $matrixA * $matrixB a valid application of
overloading. Non-commutative multiplication operations aren't uncommon
(that's why a mathematical ring only requires the addition operator to be
commutative).

The same also applies the other way around: For example PHP's default +
operator is *not* commutative (when used on arrays) and both + and * are
non-associative and non-distributive (floating point arithmetic), but you'd
probably still expect those properties from an overloaded +/- operator.

That's why I'm not sure it makes sense to have "too strict" definitions for
what is a valid overload and what isn't. I think "limited to cases where
there are clear definitions to the behavior of all overloaded operators"
and "should be for mathematical use cases only" are enough as guidelines :)

Thanks,
Nikita

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