[RFC][Dynamic class constant fetch]

Heyo,

Hi everyone

I'd like to propose a simple RFC to introduce looking up class
constants by name. We have dedicated syntax for basically all other
language constructs. This RFC aims to get rid of this seemingly
arbitrary limitation.

https://wiki.php.net/rfc/dynamic_class_constant_fetch

Please let me know if you have any thoughts.

What's the problem with using constant() for this?

Marco Pivetta

https://twitter.com/Ocramius

https://ocramius.github.io/

As it says right in the RFC:

// This:
echo Foo::{$bar};

// is way more convenient than this mess:
echo constant(Foo::class . '::' . $bar);

This is something people have mentioned a number of times with enums and dynamic case references, and seems like a good small cleanup.

--Larry Garfield

Hi Ilija,

Am 04.11.2022 um 15:25 schrieb Ilija Tovilo:

Please let me know if you have any thoughts.

Ilija

That new way of accessing class constants dynamically does not really
make things more readable for me. Maybe I just need to get used to it,
but especially that last example would make my head spin without
additional comments:

Foo::{test('foo')}::{test('bar')}; Maybe I miss the use case. What kind
of code would benefit
from this? Wouldn't just using constant() for dynamically built
constant
strings be more legible? Maybe in a separate line? In the past I used a
lot of flag constants backed by integers. A lot of these use cases have
become classes/types in their own right since. When do you use these
constants? Just my thoughts.

Dynamically building strings for syntax is almost never more legible. :-) I doubt you'd ever double them up the way some of the examples show.

In practice, the single Class::{$const} or Enum::{$name} would be the most common uses, I predict, and those are way nicer to read than the 3x longer constant() with string concat.

--Larry Garfield

Hi everyone

Sorry for the late reply.

I won't waste too many lines on usefulness as it is highly subjective.
The change will seem worth it to some people and not to others. IMO
language consistency is important and mainly what I'm striving for.

Hi Michał

Can it be extended to non class constants and additionally deprecations plan for constant() function?

I'm not sure what that syntax would look like. {$foo} is not a viable
option since it is ambiguous or rather would require arbitrary
lookahead (i.e. {$foo;} is valid syntax today). A different syntax
would be possible but inconsistent with the existing options. In any
case, this would likely require its own RFC and should be discussed
separately.

Hi Nikita

See https://www.npopov.com/2017/04/14/PHP-7-Virtual-machine.html#writes-and-memory-safety for why the order of execution is the way it is. As class constants do not support writes, these concerns do not apply, and the "normal" order can be used (as you propose).

Thank you! I remembered discussing this back when implementing the
nullsafe operator but was fuzzy on the details :) This makes more
sense to me now. I tried to clarify in the RFC.

Ilija

Hi Ilija,

I'd like to propose a simple RFC to introduce looking up class

constants by name. We have dedicated syntax for basically all other
language constructs. This RFC aims to get rid of this seemingly
arbitrary limitation.

https://wiki.php.net/rfc/dynamic_class_constant_fetch

Heads up: There hasn't been much discussion on this RFC in the last
couple of weeks, thus I'd like to start the voting phase in the next
couple of days.

Thanks for the reminder about this topic.

I'm wondering about this:

This RFC proposes no change in the interaction between class constant
fetches and the null-coalescing operator ??. That is, Foo::{$bar} ?? null;
will throw an Error if the given constant does not exist. It would be
possible to suppress this error as is done for other types of member
accesses. However, it's not clear whether this is desirable, especially for
explicit class constant fetches. This change can be made in the future with
no backwards compatibility break.

Since an argument in favor of the RFC is to replace a function call by
native syntax, wouldn't it be desired to allow the same for checking the
existence of a const? I'm thinking about defined(), which the ?? operator
would nicely replace IMHO.

Are there technical reasons to not do it in this RFC? If not, could this be
considered?

Thanks,
Nicolas