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Date: Sun, 23 Mar 2025 18:37:25 +0000
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Subject: Re: [PHP-DEV] Feedback for nullc Idea
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On 23/03/2025 12:52, Robert Chapin wrote:
> Hi PHP folks,
>
> I submitted a proposal on Monday that received no replies.  The idea 
> was about adding a functional construct nullc() that could act as an 
> inline null coalesce for a variable.  That task is currently not 
> possible in a nullc() user function, but instead requires an 
> expression like ($var ?? null) with mandatory extra parentheses.


I'm sympathetic to the problem you're trying to solve - the precedence 
of ?? isn't always helpful - but I'm not sure I like the proposed 
solution, for 3 reasons.


1) The name "nullc" is over-shortened and cryptic. The "c" looks almost 
like an accident, and it doesn't actually do anything if given a null.


2) With only one argument, it isn't really "coalescing" anything, it's 
just suppressing errors. It's telling that all your examples with ?? put 
a value other than null on the right-hand side.

If the default is not one of the normal values, the effective default 
depends on how you use it:

if (nullc($test) === 'on')
if (nullc($test) !== 'off')

In my experience, a lot of people struggle to follow logic like this, 
and it can easily lead to subtle bugs. Compare the same logic with 
explicit defaults:

if (nullc($test, 'off') === 'on')
if (nullc($test, 'on') !== 'off')


3) The function-like syntax doesn't seem to gain us much; it has to be a 
language construct not a true function, so it won't be usable with 
things like array_map, and with two arguments, nullc($foo, $bar) and 
($foo ?? $bar) look very similar.


All of which makes me look to the COALESCE function from SQL:

- The name is short but not cryptically abbreviated, and will be 
familiar to most PHP users.
- The function is variadic - you can pass just one argument, but can 
also pass three, or ten.
- The parameters are evaluated lazily, like they would be with an operator.

I've seen and implemented many variations of this in userland, although 
obviously using `$arg !== null` rather than `isset($arg)`.

There is a small risk that some people might have an existing function 
with different behaviour, e.g. a test on "emptiness" with `$arg != 
false`, and need to rename it when upgrading PHP.


I'm still only lukewarm on including it, because it's mostly just 
reminding you to include a pair of parentheses:

if (($_POST['input'] ?? null) === 'yes') echo 'success';
if (coalesce($_POST['input']) === 'yes') echo 'success';
if (coalesce($_POST['input'], null) === 'yes') echo 'success';

if (($_POST['input'] ?? $_GET['input'] ?? 'N/A') !== 'N/A') echo 
'meaningful value provided';
if (coalesce($_POST['input'], $_GET['input'], 'N/A') !== 'N/A') echo 
'meaningful value provided';



-- 
Rowan Tommins
[IMSoP]