Meta: it would make my year if we could get one of these compiler
discussions happening once a week on a public forum like this, both for
better basic understanding about why some of these concepts are not
trivial, and for better visibility into what else is going on in the
process of continuing to improve and grow GWT.
On Mon, Apr 18, 2016 at 12:49 PM 'Ray Cromwell' via GWT Contributors <
google-web-toolkit-contributors@googlegroups.com> wrote:
> I'm ok with restricting them to @JsFunction java8 lambdas. That's
> likely to be the common path for web oriented code for event handling.
>
>
> On Mon, Apr 18, 2016 at 10:47 AM, 'Roberto Lublinerman' via GWT
> Contributors <google-web-toolkit-contributors@googlegroups.com> wrote:
> > That is why I am saying that it will be easy to do for JsFunctions but
> due
> > to Java semantics (regular) lambdas are just not plain functions and
> thus I
> > don't think there is much to gain there.
> >
> > I don't think there is much to gain on the regular lambdas. There are 2
> > different ways we can handle them and reduce a bit of the generated code
> but
> > I don't think there is a lot of potential ways.
> > 1) do not generate anonymous inner classes, rather have the make lambda
> > factory take all the required parameters, i.e. castmap.
> > 2) create an anonymous innerclass based on the class/interface that is
> being
> > extended/implemented when a lambda for that is seen. In that way if an
> > interface is used with many lambdas there is only one supporting class
> > instead of many.
> >
> >
> > On Mon, Apr 18, 2016 at 10:22 AM, 'Ray Cromwell' via GWT Contributors
> > <google-web-toolkit-contributors@googlegroups.com> wrote:
> >>
> >> I understand, but the trampolines cause bloat, and if you're
> >> suggesting treating all non-JsFunction Java8 lambdas as JsFunctions as
> >> far as code-gen is concerned, then you would not be able to make the
> >> following code work:
> >>
> >> foo(Callable x) { bar(x); }
> >> foo(Runnable x) { bar(x); }
> >>
> >> bar(Object x) { if (x instanceof Callable) { print("it's a callable");
> >> } else if (x instanceof Runnable) { print("It's a runnable"); } }
> >>
> >> You need a castMap for that.
> >>
> >>
> >> On Mon, Apr 18, 2016 at 10:17 AM, 'Roberto Lublinerman' via GWT
> >> Contributors <google-web-toolkit-contributors@googlegroups.com> wrote:
> >> > The point is that for JsFunctions you DON'T actually need to do the
> >> > makeLambda(). JsFunction was designed to be able to pass JS functions
> to
> >> > JAVA so there is a code path for that and we can exploit it for
> >> > JsFunction
> >> > lambdas.
> >> >
> >> > So x -> 42 + capture will be represented in the JAva AST as
> >> > class X {
> >> > {
> >> > ..... new X$0(capture);
> >> > }
> >> > // Synthetic lambda method
> >> > int lambda_f(capture, x) {
> >> > return 42 + capture;
> >> > }
> >> >
> >> > // Lambda function implmenetation. Nothing needs to be emitted for
> this
> >> > in
> >> > JS
> >> > class X$0 implements JsFunctionInterface {
> >> > capture;
> >> > X$0(capture) {
> >> > this.capture = capture;
> >> > }
> >> >
> >> > int m(x) {
> >> > X.lambda_f(this.capture, x);
> >> > }
> >> > }
> >> >
> >> >
> >> > In the JS ast we do
> >> >
> >> > new X$0(capture) --> function(x) { X.lambda_f(capture, x) }
> >> >
> >> > So we don't need makeLambda or anything else; we can just treat
> >> > JsFunciton
> >> > implementation as if they were functions passed in from JavaScript
> where
> >> > object methods will go through the regular trampoline into the "JSO"
> >> > implementation.
> >> >
> >> >
> >> >
> >> >
> >> > On Mon, Apr 18, 2016 at 9:55 AM, 'Ray Cromwell' via GWT Contributors
> >> > <google-web-toolkit-contributors@googlegroups.com> wrote:
> >> >>
> >> >> That seems similar to my proposal, only you're doing it in GenJsAST.
> >> >> You'll still need to the makeLambda() trick to allow it to work as a
> >> >> regular obejct as well, with hashCode()/equals()/getClass()
> >> >> properties, as well as castMap installed. But if you use static
> method
> >> >> delegation, the size won't be as ideal if the static method doesn't
> >> >> inline.
> >> >>
> >> >> You want something like x -> 42 + capture to compile to
> >> >> makeLambda(function(x) { return 42 + capture }, castMap, classLit),
> >> >> not function(x) { return Class.foo(capture, x); } do you not?
> >> >>
> >> >>
> >> >> On Mon, Apr 18, 2016 at 9:49 AM, 'Roberto Lublinerman' via GWT
> >> >> Contributors <google-web-toolkit-contributors@googlegroups.com>
> wrote:
> >> >> > The scheme I had in mind does not modify much the Java AST
> >> >> > representation
> >> >> > but is more in the lowering to the JsAST, basically it boils down
> the
> >> >> > the
> >> >> > following:.
> >> >> > 1. You create the lambda body as a static method of the class where
> >> >> > it
> >> >> > appears. This static method has all captures as parameters (thiis
> is
> >> >> > very
> >> >> > similar as we are doing today).
> >> >> > 2. Synthesize an anonymous inner class that implement the
> JsFunciton
> >> >> > (also
> >> >> > same as we are doing now). The compiler in the java phase sees this
> >> >> > as
> >> >> > an
> >> >> > innerclass.
> >> >> > 3. Emit the following code for new
> JsFuncitonimplementation(capture1,
> >> >> > capture2) as function(par1, par2, parn) ->
> >> >> > {Class.lambdaFunctionImplementation(capture1, capture2, par1, par2,
> >> >> > parn) }.
> >> >> > 4. Do not emit any code for the anonymous inner class.
> >> >> >
> >> >> > This function will behave as if it was a native function passed
> from
> >> >> > JS,
> >> >> > and
> >> >> > object methods will work in the same way. Of course the devil is in
> >> >> > the
> >> >> > details.
> >> >> >
> >> >> >
> >> >> > On Mon, Apr 18, 2016 at 9:34 AM, 'Ray Cromwell' via GWT
> Contributors
> >> >> > <google-web-toolkit-contributors@googlegroups.com> wrote:
> >> >> >>
> >> >> >> Seems to me this'll be tricky to pull off. The GWT compiler has no
> >> >> >> notion of captured scope. If you want to create a class type that
> >> >> >> represents a lambda, but which doesn't actually get output as a
> >> >> >> class,
> >> >> >> you'd have to change many many parts of the compiler.
> >> >> >>
> >> >> >> I think perhaps the best thing you could do would be a kind of
> >> >> >> 'peephole' optimization pass. After all Java optimization passes
> >> >> >> have
> >> >> >> run, and after JS has been generated, go through using pattern
> >> >> >> matching to find "new generatedlambda(captured variables)" and
> >> >> >> replace
> >> >> >> it with "makeLambda(classtype, castMap, classLiteral,
> function(...)
> >> >> >> {
> >> >> >> body of single abstract method })". Then hope the JS dead code
> >> >> >> pruning
> >> >> >> removes the unused inner class.
> >> >> >>
> >> >> >> I think if you try to model this in the Java AST it would impact
> too
> >> >> >> much
> >> >> >> stuff.
> >> >> >>
> >> >> >>
> >> >> >> On Mon, Apr 18, 2016 at 9:04 AM, 'Roberto Lublinerman' via GWT
> >> >> >> Contributors <google-web-toolkit-contributors@googlegroups.com>
> >> >> >> wrote:
> >> >> >> > We accept patches :)
> >> >> >> >
> >> >> >> > On Sun, Apr 17, 2016 at 8:40 PM, Paul Stockley
> >> >> >> > <pstockl...@gmail.com>
> >> >> >> > wrote:
> >> >> >> >>
> >> >> >> >> Given that it will be realistically a couple of years before
> most
> >> >> >> >> large
> >> >> >> >> projects could migrate to J2CL, it would be really nice to
> have a
> >> >> >> >> more
> >> >> >> >> optimal code generation for lambda's, especially for
> JsFunction.
> >> >> >> >> When
> >> >> >> >> 2.8
> >> >> >> >> gets released, I think people will really start taking
> advantage
> >> >> >> >> of
> >> >> >> >> existing
> >> >> >> >> JS libraries that really heavily use functions.
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> On Friday, April 15, 2016 at 12:03:12 PM UTC-4, Roberto
> >> >> >> >> Lublinerman
> >> >> >> >> wrote:
> >> >> >> >>>
> >> >> >> >>> It should not be hard to make JsFunction lambdas more terse,
> but
> >> >> >> >>> there
> >> >> >> >>> are no plans for GWT 2.x.
> >> >> >> >>>
> >> >> >> >>>
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