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From Daniel Sun <realblue...@hotmail.com>
Subject 答复: Lambda vs. Closure (was: [VOTE] Apache Groovy Roadmap)
Date Tue, 07 Feb 2017 16:39:21 GMT
Hi Jesper,


  *   I'm not sure why we need a separate discussion.



If most of us want the current lambda expression(based on closure), we need not thrash out
how to implement Java-lambda semantics 😉


  *   We have a basic choice: 1) Use Java-lambda semantics or 2) Groovy-closure semantics.
As a variation on 2, we can add some help for people pasting Java code into a Groovy program.

Agreed.

P.S.     I have not seen your above words…


Cheers,
Daniel.Sun

发件人: 孙 岚<mailto:realbluesun@hotmail.com>
发送时间: 2017年2月7日 23:49
收件人: Jesper Steen Møller [via Groovy]<mailto:ml-node+s329449n5738482h0@n5.nabble.com>
主题: 答复: Lambda vs. Closure (was: [VOTE] Apache Groovy Roadmap)

Hi Jesper,

     Gotcha 😊
     For me, I don’t like two versions of lambda expression… it will confuse developers.

Cheers,
Daniel.Sun

发件人: Jesper Steen Møller [via Groovy]<mailto:ml-node+s329449n5738482h0@n5.nabble.com>
发送时间: 2017年2月7日 23:44
收件人: Daniel Sun<mailto:realbluesun@hotmail.com>
主题: Re: Lambda vs. Closure (was: [VOTE] Apache Groovy Roadmap)


On 7 Feb 2017, at 16.27, Daniel Sun <[hidden email]</user/SendEmail.jtp?type=node&node=5738482&i=0>>
wrote:
     To fully support *real* lambda expression, (to be honest)currently I have no idea how
to generate bytecode for it. In addition, supporting Static Compilation will be another big
work…
A real lambda expression is implemented in Java as an invokedynamic call which makes use of
a bootstrap method calling into a class called the LambdaMetafactory (https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/LambdaMetafactory.html)
, and puts the body of the lambda expression into a hidden method on the class. The LambdaMetafactory
sets up the magic class which holds any escaped variables and implements the functional interface.
To work, it requires EXACT type information, so it's only possible to do this in static compilation.



  *   For instance, we could warn the user if the lambda referred to 'this' or 'super' directly.

I think ‘this’ and ‘super’ can be referred but developers should not change its resolve
strategy, so we can forbidden the scenario by syntax check 😊

     I would like to open a new discussion based on our discussion in the dev-list later and
wish others would think same with us to accept the closure with lambda syntax

I'm not sure why we need a separate discussion.
We have a basic choice: 1) Use Java-lambda semantics or 2) Groovy-closure semantics. As a
variation on 2, we can add some help for people pasting Java code into a Groovy program.

Generating faster/tighter code for lambdas (or even closures) can be implemented as a separate
task, the two aren't really interconnected, since the Groovy closure is so versatile to begin
with.

-Jesper

发件人: <a href="x-msg://13/user/SendEmail.jtp?type=node&amp;node=5738481&amp;i=0"
target="_top" rel="nofollow" link="external" class="">[hidden email]
发送时间: 2017年2月7日 23:10
收件人: <a href="x-msg://13/user/SendEmail.jtp?type=node&amp;node=5738481&amp;i=1"
target="_top" rel="nofollow" link="external" class="">[hidden email]
主题: Lambda vs. Closure (was: [VOTE] Apache Groovy Roadmap)

(changing the subject so we don't disrupt the main discussion)

Not quite 😔

The changes in Java to support Lambdas are much deeper than just how the Metafactory is invokedynamic'ed,
as it changes how type inference and overload resolution is done. Same as with the issues
we discussed a while back around method references: Supporting Java8 semantics in the Groovy
compiler is a very big task, as we just don't have the type information available.

I would much rather suggest supporting the lambda syntax with groovy semantics, but add warnings
if we detect that the code may rely on Java lambda semantics. For instance, we could warn
the user if the lambda referred to 'this' or 'super' directly.

-Jesper

On 7 Feb 2017, at 16.00, Daniel Sun <<a href="x-msg://13/user/SendEmail.jtp?type=node&amp;node=5738478&amp;i=0"
target="_top" rel="nofollow" link="external" class="">[hidden email]> wrote:

Hi Jochen,

That’s great!
Paul and Graeme are both afraid of future breaking changes of groovy’s lambda expression,
which is currently based on closure. If we could generate *real* lambda bytecode for LambdaExpression,
groovy’s lambda expression will behave same with Java8’s at runtime😊

Cheers,
Daniel.Sun

发件人: <a href="<a href="x-msg://12/user/SendEmail.jtp?type=node&amp;amp;node=5738477&amp;amp;i=0"
class="">x-msg://12/user/SendEmail.jtp?type=node&amp;node=5738477&amp;i=0" target="_top"
rel="nofollow" link="external" class="">[hidden email]
发送时间: 2017年2月7日 22:23
收件人: <a href="<a href="x-msg://12/user/SendEmail.jtp?type=node&amp;amp;node=5738477&amp;amp;i=1"
class="">x-msg://12/user/SendEmail.jtp?type=node&amp;node=5738477&amp;i=1" target="_top"
rel="nofollow" link="external" class="">[hidden email]
主题: Re: [VOTE] Apache Groovy Roadmap



On 07.02.2017 14:44, Daniel Sun wrote:
> Hi Cédric,
>
>       It seems that too many choices are a annoying problem, but I
> believe we can conquer it sooner or later ;)
>       BTW, is it possible to keep groovy' lambda expression as it
> is(i.e. groovy closure with lambda syntax) but generate *real* lambda
> bytecode for
> it(https://github.com/apache/groovy/blob/parrot/src/main/org/codehaus/groovy/ast/expr/LambdaExpression.java)?

sure, you should make a visitLambdaExpression similar to
visitClosureExpression and change our visitors

bye Jochen


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