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Date: Fri, 22 Nov 2013 10:09:48 +0900
Message-ID: <CAGa2bXYmV3+BuowZTBdQjgGoWqiZhYegd8w5208Mso5SAoq=Ew@mail.gmail.com>
To: Bob Weinand <bobwei9@hotmail.com>
Cc: List PHP Mailing List <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=089e013d1a941327c704ebb9ae78
Subject: Re: [PHP-DEV] [RFC] [VOTE] Constant scalar expressions
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Hi all,

On Thu, Nov 21, 2013 at 6:11 AM, Bob Weinand <bobwei9@hotmail.com> wrote:

> That'd just be outside of this RFC's scope:
>
> const ABC = [1, 2];
>
> is currently not allowed. Also you can't write ABC[0]. That'd be a whole
> other RFC to add array support for constants.
>

I understand it requires new codes(and flag) to make a constant
array/object.


> So we could enable it for (static) properties, but why should we?
>
> Additions of arrays would be the only valid operation, but can you imagine
> _any_ use case where we'd need that when the only dynamic operands (
> constants) can't be arrays?
>

I just thought constant array/object is useful for application settings, etc
that should not be changed.

Anyway, constant variables are useful for VM/op code optimization.

include('foo.php'); // const a = 123;
const b = a;

is allowed currently. We may restrict this behavior only to the same file,
so that VM/op code optimization can be done.

Currently, no expression is allowed with 'const'. Defining 'const' using
another constant with the same value is useless. It's a bad coding practice
in many case, I suppose.

I understand use cases of scalar expressions with constants, but I'm
concerned
loosing door for further optimizations. (e.g. $x = $x + 123 is faster than
$x = $x + a,
where a is 123 in constant var hash)

We may be better to restrict expressions with constants only to the same
file
even if we loose some benefits/flexibility in user code.

Is this discussed?

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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