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Date: Wed, 14 Aug 2013 06:44:46 -0400
Message-ID: <CAAyV7nH-+9U25GkpC0afgomR5T_7MPfCzvnhJLxOeZHuOL4=+A@mail.gmail.com>
To: Stas Malyshev <smalyshev@sugarcrm.com>
Cc: Julien Pauli <jpauli@php.net>, "internals@lists.php.net" <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=047d7b5d870fc9e67704e3e60b03
Subject: Re: [PHP-DEV] [RFC] Constant Scalar Expressions
From: ircmaxell@gmail.com (Anthony Ferrara)

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Stas,


On Wed, Aug 14, 2013 at 5:01 AM, Stas Malyshev <smalyshev@sugarcrm.com>wrote:

> Hi!
>
> >> https://wiki.php.net/rfc/const_scalar_expressions
>
> I like the idea, but absence of constant support makes this thing much
> less useful, as you can't do things like:
>
> public $angle = M_PI/2;
>
> I think this is one of the reasons this idea was never implemented -
> because without constant support you're limited to doing things that are
> quite obvious and trivial.
>

Yeah, having constants in those expressions would be great. If only
constants in PHP were actually constant...

But this win is really cheap (a trivial change to the parser), so I figured
it was worth proposing separately. If we want to add the opcode stream
later to do expressions for constant values, we can. This just gives us the
quick win today of allowing relatively trivial, but important expressions.

The biggest wins I see are in power-of-2 math:

class Foo {
    const FLAG_1 = 1 << 0;
    const FLAG_2 = 1 << 1;
    const FLAG_3 = 1 << 2;
    const FLAG_4 = 1 << 3;
    const FLAG_5 = 1 << 4;
    const FLAG_6 = 1 << 5;
    const FLAG_7 = 1 << 6;
}

And in other complex formulas where having the self-declaration adds
semantic meaning.

Now, as far as if it's worth while making the change without constant
support, that's for each of us to decide. I think it is, but if you don't,
that's cool too.

Thanks

Anthony

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