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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