Part of the problem would come from figuring out how to call from JS back
into Java - if you called resolve(null), was null a T or was null a
Promise? And from JS, how could you typecheck to figure out whether to call
the resolve_1(value) or resolve_2(promise)?
Its also possible in JS to call with too many arguments, and if you call
with not enough, they get a null value, so we'll have a resolve_0() in
there too - but if the wrong number of arguments are there, which do you
invoke?
So, rather than JsInterop being a method lookup layer to translate to Java
method call semantics, JsInterop uses JS semantics and lets you use them
from Java. Just as you would write your resolve method in JS, you should
write it in Java - take the object, and based on the value, decide what to
do with it.
Now I realize that this doesn't directly apply to your case, since you want
to do it the other way around - pass an object implemented in JS into Java
and interact with it there, but JsInterop provides functionality to work in
both directions, and I'm not certain how you could tell JsInterop that you
will never implement an interface in Java, or if that is functionality that
we want. Instead, you could have a single method resolve(Object), and let
JS sort it out, whether you call it with null, a value, or another promise.
(Disclaimer, I'm not a JsInterop expect, but I'm trying to learn quickly.)
On Sat, Aug 27, 2016 at 8:51 AM Arnaud TOURNIER <ltea...@gmail.com> wrote:
> Hi,
>
> I am playing with js Promises and maybe there's a problem with JsInterop
> or i don't understand something.
>
> When wrapping the promises with JsInterop, i come to define the Resolver
> interface which represents the resolving callback that is given when
> constructing a promise. In Javascript it is a function and not an object,
> so the interface has the @JsFunction annotation.
>
> Here is the Resolver interface (inspired from the TypeScript definition of
> Promises...) :
>
> @JsFunction
> @FunctionalInterface
> public interface Resolver<T>
> {
> void resolve( T value );
> }
>
> Since the Javascript "resolve" function can be called without parameters
> and also with a Promise instead of a value, i would like to make those
> versions available in the interface.
>
> But the @JsFunction annotation prevents from having this :
>
> @JsFunction
> public interface Resolver<T>
> {
> void resolve();
>
> void resolve( T value );
>
> void resolve( Promise<T> value );
> }
>
> That's because it allows only one method in the annotated interface.
>
> That is what i don't understand : AFAIK, the gwt compiler has to call the
> same function in the same way for the three declared methods (because of
> the semantic of the @JsFunction annotation), just changing the calling
> parameters. So i don't understand why is there the limitation of having
> only one method allowed in @JsFunction interfaces... If it would it would
> give even much power to JsInterop !
>
> Could you please bring light to my misunderstanding ?
>
> Thanks !
>
> Arnaud
>
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