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Date: Mon, 27 Nov 2017 07:53:01 +0100
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Subject: Re: [PHP-DEV] C++-like function-try-block proposal
From: nikita.ppv@gmail.com (Nikita Popov)

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On Mon, Nov 27, 2017 at 5:06 AM, <enclaved@safe-mail.net> wrote:

> Greetings!
>
> I have been referred to this mailing list by
> https://wiki.php.net/rfc/howto
> as the first step to propose a language change.  I first tried to register
> on wiki.php.net as per php-src/README.SUBMITTING_PATCH in order to
> actually
> make an RFC, only to be given an error:
>
>   Writing /srv/web-wiki/dokuwiki/conf/users.auth.php failed
>
> I am proposing a patch (see attachment) to bring C++-like
> function-try-block
> shorthand syntax (http://en.cppreference.com/w/cpp/language/function-try-
> block)
> for whole-function try-catch-finally blocks:
>
>   function fuu($foo, $bar): void try
>   {
>     may_throw($foo);
>     may_throw($bar);
>
>   } catch (FuuException $e) {
>     echo $e->getMessage();
>   }
>
> Since PHP is partially influenced by C++, I believe this syntax would be
> a meaningful step in making PHP a little bit more intuitively compatible
> with C++ practices, which may prove useful for people who come to PHP from
> the C++ world (such as myself.)  The expected benefit is PHP becomes yet
> more familiar and comfortable for C++ programmers.
>
> Also, this syntax saves us one set of curly braces and an indentation
> level,
> allowing for more compact and expressive functions, and especially
> closures:
>
>   $s = preg_replace($re, $s, function (array $m): void try {
>     return find_replacement(...$m);
>   } catch (Throwable $e) {
>     return $m[0];
>   });
>
> In addition to the syntactic sugar, I would like to outline another
> possible
> merit: the very fact of such a shorthand construct existing may encourage
> programmers to write functions with a consistent approach to exception
> handling
> at whole-function level.  Each such function becomes a self-contained code
> unit
> tightly coupled with its exception handling logic, the programmer's intent
> clearly outlined by the use of the proposed construct, thereby facilitating
> code clarity and integrity and promoting a stricter and more rigid code
> style.
>
> The proposed patch makes purely cosmetic modifications to
> zend_language_parser.y
> grammar to augment plain functions, class methods, and closures to accept
> try-catch-finally blocks as their bodies in addition to regular compound
> statements.  It amounts to just a handful of lines and entails no API
> changes.
>
> I submitted my patch via the bugtracker: https://bugs.php.net/bug.php?
> id=75576
>
> Please share your thoughts.
>

I believe that the reason why C++ has function-level try-catch blocks is
that they provide the only way of catching exceptions thrown by the member
initializer list of a constructor. As PHP does not have any such
functionality, PHP has no need for function-level try-catch blocks.

I doubt that C++ introduced these as a way to save a couple of braces,
especially given that C++ does not allow the use of other, and arguably
significantly more common, control-flow statements without an explicit
function block.

Nikita

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