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Date: Sun, 28 Mar 2021 17:13:49 +0100
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Subject: Re: [PHP-DEV] [RFC] Auto-capture multi-line closures and short
 functions take 2
From: rowan.collins@gmail.com (Rowan Tommins)

On 25/03/2021 16:25, Larry Garfield wrote:
> So in conclusion, it seems the reasons closures weren't auto-capture always were:
>
> 1) Possible performance concerns that are no longer relevant.
> 2) Avoid surprise references.
> 3) Allow users to capture by value or by reference.


I wasn't involved in the discussion when anonymous functions were first 
added, but I was during the discussions that led to the current arrow 
functions.

I think it's important context that multi-statement closures were 
originally included and explicitly removed, precisely because automatic 
capture was always controversial.

It is perfectly reasonable to re-visit the topic now, but it is not, as 
some seem to be implying, one that has already been agreed in principle.


Bob's original "Short Closures" RFC [1] in 2015 included both single 
expressions and full function bodies. As in subsequent discussions, some 
people thought implicit capture was a great feature, and others were 
concerned by it. Rasmus described it [2] as "breaking [a] longstanding 
basic tenet of the language".

There were other reasons that RFC was not accepted, mostly around 
syntax, but several people in the voting thread [3] gave automatic 
capture as a reason for voting no.

The subsequent "Arrow Functions" RFC [4] by Bob and Levi in 2017 
explicitly removed multi-statement bodies from the proposal, citing 
feedback from previous discussions. Bob confirmed in the discussion 
thread [5] that this was a deliberate design choice, because requiring 
"use" for most Closures "vastly improves readability and debuggability".

Rasmus agreed [6] that automatic capture was acceptable in the new RFC 
specifically because single-expression closures "don't typically need a 
local scope at all".

Finally, in 2019 Nikita wrote a new version of the RFC [7] which again 
left out multi-statement bodies. During the discussion [8] he considered 
adding them back in, but felt it would "add a number of complications" 
which should be addressed in a future RFC.

Several people who had previously expressed strong concerns about 
automatic capture voted "Yes" to Nikita's RFC . At least some presumably 
did so precisely because multi-statement bodies were not included.


[1] https://wiki.php.net/rfc/short_closures
[2] https://externals.io/message/87958#87969
[3] https://externals.io/message/88394
[4] https://wiki.php.net/rfc/arrow_functions
[5] https://externals.io/message/98045#98069
[6] https://externals.io/message/98045#98108
[7] https://wiki.php.net/rfc/arrow_functions_v2
[8] https://externals.io/message/104693#104738


Regards,

-- 
Rowan Tommins
[IMSoP]