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In-Reply-To: <64E00A5D.5010108@adviesenzo.nl>
Date: Sat, 19 Aug 2023 10:48:06 +0200
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To: Juliette Reinders Folmer <php-internals_nospam@adviesenzo.nl>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] Access property of object stored in a constant
From: tovilo.ilija@gmail.com (Ilija Tovilo)

Hi Juliette

> > Since https://wiki.php.net/rfc/new_in_initializers we can store
> > objects in global constants. However, we may not actually read or
> > write to the properties of those objects without first fetching the
> > constant into a local variable.
> >
> > const a = new stdClass;
> > a->b = 42; // Fatal error: Cannot use temporary expression in write context
> > $a = a;
> > $a->b = 42; // Works fine
> >
> > This issue was reported twice, so it seems like this code is generally
> > expected to work.
> > https://github.com/php/php-src/issues/10497
> > https://github.com/php/php-src/issues/11781
> >
> > I have created a patch here to add support for this syntax:
> > https://github.com/php/php-src/pull/11788
>
> I totally understand that people are trying to do this, but this still
> very much feels like scope creep.
>
> IIRC the new in initializers feature was _intended_ only for enums
> (which can't take properties). Now suddenly a "constant" would no longer
> be constant... In which case, what's the point of declaring it as a
> constant ?

This patch doesn't change the mutability of objects in constants, as
they already don't offer interior immutability. https://3v4l.org/s7rHE
This is analogous to `const` in JavaScript or `readonly` properties in
PHP, where we can't change the value of the variable (or const in this
case), but we can modify the properties of the object it's pointing
to.

I believe the main motivation for `new` in constant expressions was to
support nested attributes. Enums have their own mechanism for
instantiating cases. Since it was decided to expand the support for
`new` to global constants, I would expect it to work with other
language constructs, unless there's a good reason for it not to.

Ilija