Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:114247
To: internals@lists.php.net
References: <88c9eb5f-f80c-4869-b7f8-1b58b9e2eaa3@www.fastmail.com>
 <CAF+90c9pXNAkwUXEtoJLS7hJT0hDO3OYEjT4=91GNpwX12wTxA@mail.gmail.com>
 <CALZWoqWwh+ruvg85RbvOvWGYk8EBtaUg+G_x8SnBQ-wFHFKvbQ@mail.gmail.com>
Message-ID: <a614c272-f1d5-91f3-a141-6aa234b395eb@gmail.com>
Date: Thu, 29 Apr 2021 09:14:29 +0100
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.10.0
MIME-Version: 1.0
In-Reply-To: <CALZWoqWwh+ruvg85RbvOvWGYk8EBtaUg+G_x8SnBQ-wFHFKvbQ@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-GB
Subject: Re: [PHP-DEV] [RFC] Auto-capture multi-line closures and short
 functions take 2
From: rowan.collins@gmail.com (Rowan Tommins)

On 28/04/2021 23:00, Nuno Maduro wrote:
> Concerning point 2: Developing some sort of static analysis that can infer
> what needs to be captured may be problematic. First, that won't be
> consistent with the way auto-capture currently works in PHP (one-line short
> closures).


The question is, how do we decide which variables are local, and which 
are captured? Options include:

1) All variables are captured, except those declared local. This is 
common in other languages, but has no syntax in PHP.
2) All variables are local, except those declared captured. This is what 
the "use" clause is for in the current "long" closure syntax.
3) All variables are captured, there is no local scope. This is 
effectively what PHP's single-expression closures use.
4) All variables are captured, unless provably written before read. This 
is what I think Nikita is suggesting.

Option 3 is the easy option, and is currently "good enough" because it's 
rare to need a purely local variable within a single expression. For a 
full function body, local variables are much more likely, so we now need 
to think about the question more carefully.

Without a keyword like "var" to declare it, I think most users would 
assume that an initialisation like "$foo=null;" at the top of their 
closure would make a variable local.

Regards,

-- 
Rowan Tommins
[IMSoP]