Re: Object Type Casting Reloaded

On Mon, Apr 22, 2019 at 11:48 PM Benjamin Morel <benjamin.morel@gmail.com> wrote: > Hi internals, > > I'd like to revive an old discussion > <https://externals.io/message/67131> > about > object type casting. > > The idea would be to allow (ClassName) casting: > > $service = (EmailService) $diContainer->get('email.service'); > > The above code would throw a TypeError if the value is not an instance of > the given class. I see the following advantages: > > - Type safety: we can be sure that the value is of the correct type or that > we'll get an Error. This syntax allows to fail early if the variable > happens to not be of the expected type, and avoids much more verbose > checks; > - Static analysis: IDEs and static code analysis tools can now understand > the type of the variable, without having to resort to @var > annotations. > > These combine into a third advantage: readability. Today's equivalent of > the above one-liner could be: > > /** @var EmailService $service */ > $service = $diContainer->get('email.service'); > if (! $service instanceof EmailService) { > throw new TypeError('Expected instance of EmailService, ...'); > } > > Which is a lot of boilerplate code that could be easily avoided by > introducing this new syntax. > > Before moving forward and working on a formal RFC, I'd like to hear your > thoughts: what's your early feeling about this? Did I miss other > discussions around this subject? Are there any technical issues that come > to mind? Could this feature help the upcoming JIT compiler produce more > efficient machine code by knowing the type of the variable at compile time? > etc. > > Note: "casting" might not be the perfect name here as what we're really > doing is a type check, but this reuses the type casting syntax and > resembles Java's object casting. > > Thank you, > Ben > Without commenting on the rest of the proposal: It's not possible to use (ClassName) as a cast syntax, because it is ambiguous. For example (Foo) [$x] is already valid syntax (fetch constant Foo and take index $x), or (Foo) +$bar, etc. The only reason why (int) etc are okay is because we treat the whole (int) as a single token, something we can't do in general (because it would break foo(Foo)). Nikita