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Date: Sat, 23 Nov 2013 00:37:39 +0100
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To: Tjerk Meesters <tjerk.meesters@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Power function as operator
From: nikita.ppv@gmail.com (Nikita Popov)

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On Fri, Nov 22, 2013 at 5:58 PM, Tjerk Meesters <tjerk.meesters@gmail.com>wrote:

> Hi,
>
> To challenge myself I had tasked myself to introduce a new operator and
> opcode to the language; now that I'm done with it, I wanted to measure the
> response on the list to actually get it merged before writing an RFC.
>
> My work can be found here:
> https://github.com/datibbaw/php-src/compare/pow-operator
>
> It introduces the pow() function as an operator ** (double asterisk), as
> can be found in languages such as Python (with perhaps the notable
> difference that it's right associative there).
>
> The logic gets exposed via the ZEND_POW opcode and all the logic that went
> into pow() itself is copied into it. The exceptions are that an expression
> such as [] ** 2 (squared empty array) will cause a fatal error because the
> operands are incompatible, whereas pow([], 2) would give 0.
>
> Why this operator? Basically because:
> 1) it's shorter (the keyboard rejoices).
> 2) it's faster (no ZEND_CALL).
> 3) it's found in other languages too.
>
> I've only implemented one of the test suites; there are quite a few for
> just one function, but when needed I can add those others as well.
>
> Btw, changes to vld aren't pushed yet.
>
> Let me know!
>

I don't really see a need for this operator in PHP. From my experience
pow() isn't some particularly commonly used function, so I don't think it
needs its own operator. (But I don't think that adding it would
particularly hurt either...)

Anyway, if this is added I would strongly recommend to make the operator
non-associative. I have no idea how Python came up with the idea to make **
right-associative, which violates basic programming language design rules
(all binary non-assignment operators are left-associative) and goes against
(at least my) common sense, but now that they made the choice it's likely
unwise to deviate from it by making it left-associative in PHP (see ternary
operator mess...) So I think making it non-associative makes for a safe
middle ground. This will cause 2 ** 3 ** 2 to throw an error and require
you to group it as either (2 ** 3) ** 2 or 2 ** (3 ** 3). Less ambiguity.

Nikita

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