Property Hooks Discussion

On Fri, 31 Mar 2023 at 09:57, Robert Landers landers.robert@gmail.com
wrote:

Hello,

I couldn't find the thread about Property Hooks
(https://wiki.php.net/rfc/property-hooks) -- I think it got embedded
in various places? Or maybe my search-fu in gmail is failing me.

The RFC is in "Draft" status rather than "In Discussion", so hasn't been
announced yet, and may not be ready for discussion.

I'll leave it up to Ilija and Larry to say whether your question is
something they know the answer to, or if it's a "known unknown".

Regards,

Rowan Tommins
[IMSoP]

Hi Robert!

On Fri, Mar 31, 2023 at 10:57 AM Robert Landers
landers.robert@gmail.com wrote:

I couldn't find the thread about Property Hooks
(https://wiki.php.net/rfc/property-hooks) -- I think it got embedded
in various places? Or maybe my search-fu in gmail is failing me.

As Rowan has mentioned, you couldn't find an e-mail because it hasn't
actually been announced yet. Larry and I are still working on the
details.

What would happen with the following class:

class BigNumbers {
public \Gmp $myNumber {
beforeSet(int|string $value) {
return gmp_init($value);
}
}
}

We haven't fully decided on whether we want to allow types in hook
parameters, or whether the type should be implicit. The main
motivation for allowing types is that one could accept broader types
in and convert the value to the property target type. But I'll need to
verify the technical feasibility before we make this decision.

$x = $y = $z = 1;

$x === $y && $y === $z;

I'm not quite sure what this means, as this doesn't involve hooks or properties.

Ilija

Hello,

I couldn't find the thread about Property Hooks
(https://wiki.php.net/rfc/property-hooks) -- I think it got embedded
in various places? Or maybe my search-fu in gmail is failing me.

Anyway, I was reading it carefully and I had a couple of questions.

What would happen with the following class:

class BigNumbers {
public \Gmp $myNumber {
beforeSet(int|string $value) {
return gmp_init($value);
}
}
}

Would $bigNumber->myNumber = gmp_init('25') throw an error because it
isn't a string|int? Can hooks only accept the type they are setting
or any type?

In other words, will it be possible for this to no longer be true (I'm
not sure it is always true now, fwiw):

$x = $y = $z = 1;

$x === $y && $y === $z;

This looks like a very powerful change to the language and I'm really
looking forward to using it!

As Rowan said, this is a "known unknown" at the moment, and one of the reasons the RFC hasn't been officially put forward yet. (Expect that soon.)

As it is right now, the value beforeSet receives MUST be the same as the property is typed as. You're not allowed to declare a type yourself; the property type is implied. However, that still would allow you to narrow a type yourself in practice. The RFC has an example or two of that with strings -> UString objects.

We are considering (and I would favor, if it can be done cleanly) allowing the beforeSet hook to accept a contravariant (wider) type than the property type, but still be required to return exactly the type of the property. That would allow, for instance:

class Foo {
public int $val { beforeSet(int|string $new) => (int) $new; }
}

That is, you can accept a wider set of compatible types and then, in beforeSet, fold that down to the type of the property. The type of the property is still guaranteed to be the only thing you get on read.

That would mean the following as a side effect:

$f = new Foo();
$val = '5';
$f->val = $val;
$f->val === $val; // false, because different types!

Personally I think that's acceptable for the flexibility it gives; the point of hooks is primarily to be "a thing you can add to a property in the future without having to precreate a method just in case", you can already do the above behavior with a method quite easily. So being able to do the same with hooks (and thus obviate another "just in case" reason to add a verbose but pointless method on the off chance you need it in the future) seems reasonable.

There might be other edge cases we haven't thought of yet; right now that feature is pending on Ilija making sure it could even work, which is a prerequisite for including it, obviously. :-)

--Larry Garfield