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Date: Sat, 12 Nov 2016 14:59:16 +0100
Message-ID: <CAF+90c95k53sRbcNqNLgTvr1GqwOvw85sPSRhPFEbnqz5EwBsQ@mail.gmail.com>
To: Joe Watkins <pthreads@pthreads.org>
Cc: "Christoph M. Becker" <cmbecker69@gmx.de>, PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a11474194300c3605411b0301
Subject: Re: [PHP-DEV] Re: C89 vs. C99
From: nikita.ppv@gmail.com (Nikita Popov)

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On Sat, Nov 12, 2016 at 2:21 PM, Joe Watkins <pthreads@pthreads.org> wrote:

> Morning Nikita,
>
> All good points, that it's hard to refute.
>
> However, right now, I know where all variables that are going to be used
> are declared, no matter the size of the function or it's complexity. If not
> at the very top, eyes get good at scanning for blocks.
>
> What I don't want is to have to scan already complicated code to find out
> when a variable was declared.
>
> We need to have rules of thumb, and unless someone can defend their use
> rigorously, I would say the rule of thumb that code shouldn't be mixi ought
> to be followed. At least it ought to be followed in the top layer of PHP
> (anything inside a PHP|ZEND_FUNCTION and such).
>
> A defence of elegance is legitimate, so long as their use does genuinely
> increase elegance. Such examples exist, but I think more examples of mixi
> code being harder to follow exist ...
>
> Cheers
> Joe
>

I have the feeling that we both sort-of agree, but are really talking about
different things.

There are two ways in which you can have code mixed with declarations. The
first one is within a single "basic block", like this:

    int a = ...;
    b = ...;
    int c = ...;
    a = ...;
    float d = ...;
    // ...

I can totally see how some many people might find this kind of code to be
objectionable.

However, the use-case that I have in mind is different -- it's the case
where declarations **are** at the top of a block -- but its the top of a
basic block in terms of control flow, not a block in terms of C syntax. To
clarify what I mean by that: For a compiler (and arguably, a programmer),
the control flow of

    if (...) {
        return;
    }

    // Basic block starts here, but not C block
    type var = ...;

and of

    if (...) {
        return;
    } else {
        // Basic block starts here, and C block
        type var = ...;
    }

is the same. The declaration in both cases is at the top of a control-flow
block. It just doesn't happen to coincide with a syntactic C block.

This is the case I'm interested in.

Anyway, I'll just leave this gem from our codebase here:
https://github.com/php/php-src/blob/master/ext/standard/http_fopen_wrapper.c#L114
(Some of those variables have 500 lines of code between declaration and
first use)

Thanks,
Nikita

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