RFC: Functional Interfaces

Hi!

2016-04-19 11:21 GMT-04:00 Larry Garfield larry@garfieldtech.com:

Dmitry Stogov wrote on 19/04/2016 15:48:

callable-type is much simpler solution for this use-case.
Usage of Interfaces to check function prototypes is a bit tricky, but
yes, this is a possible use-case.
Do you like to work with framework, that use this trick for every
callback?

If you don't use __invoke as the function name, you can have a single
class implement multiple contracts, e.g. to register for more than one
event type with different signatures.

I guess if you had callable-types and union types, you could get the
best of both worlds:

interface UserEventCallbackInterface {
public function handleUserEvent(UserEvent $event): boolean;
}
public function registerCallback(EventCallbackInterface|callable(Event):
boolean $handler) { ... }

The implementation has to be a bit fiddlier here, because you need to
sometimes call $handler->handleUserEvent($event) and sometimes
$handler($event); with a functional interface, the engine makes
$handler->handleUserEvent($event) work for you. The cost is that the call
site has to be a bit more verbose to specify the interface, rather than
implicitly meeting the contract.

I believe Joe has both $handler->handleUserEvent($event) and
$handler($event) cases covered already. This means that
$handler->handleUserEvent($event), $handler() and $handler->__invoke($event)
should be 100% equivalent.

Regards,

Which is why I'm not sure I like that approach, because the place I then
call $handler needs to have a conditional in it. There's another RFC that
was posted to Twitter but hasn't made it to the list yet that seems to
solve this better:

https://wiki.php.net/rfc/callable-types

(My apologies to the authors if they aren't done with it; it's on the wiki
so I'm assuming it's safe to mention in public.)

Yes, it it's ok to mention the RFC. We are going to move it to discussion
phase ASAP some minor issues get a fix :)

That allows just the callable-type syntax (which I presume is what you're
referencing), but you can then pass an object in using []-callable syntax:
[$handler. 'handleUserEvent'], and then registerCallback() doesn't care if
it was a function, method, closure, or whatever else. It can just () it.

--
--Larry Garfield

Larry Garfield wrote on 19/04/2016 16:21:

Which is why I'm not sure I like that approach, because the place I
then call $handler needs to have a conditional in it. There's another
RFC that was posted to Twitter but hasn't made it to the list yet that
seems to solve this better:

https://wiki.php.net/rfc/callable-types

I'm not sure which approach you mean, but in Joe's proposal, you always
call $handler as though it was an object implementing the interface;
have a look at the ILog example in the RFC.

With a typed callable, you can always invoke as $handler(...) will work,
but the implementer can't create an object that meets more than one
contract, because they can only provide one __invoke method.

interface UserEventCallbackInterface {
public function handleUserEvent(UserEvent $event): boolean;
}
interface CommentEventCallbackInterface {
public function handleCommentEvent(CommentEvent $event): boolean;
}

class Logger implements UserEventCallbackInterface,
CommentEventCallbackInterface { ... }
$logger = new Logger;

$simple_user_handler = function(UserEvent $event) implements
UserEventCallbackInterface: boolean { ... }

In Joe's proposal, $logger and $simple_user_handler can be used
interchangeably by calling $handler->handleUserEvent(...); the receiving
code doesn't need to do anything special to accept the closure form,
because the engine transforms it into the required object.

Regards,

Rowan Collins
[IMSoP]