invokedynamic and subclasses

[Rémi Forax]

Hi Mike, 
i've compiled a small list of patterns,
  https://code.google.com/p/jsr292-cookbook/

take a look to the first inlining cache example.

cheers,
Rémi 

Le 24 juin 2015 14:19:32 CEST, Mike Jarmy <mjarmy at gmail.com> a écrit :
>I've been experimenting with invokedynamic in a compiler for a dynamic
>language
>that I'm working on, and I've run into a problem that I'm having
>difficulty
>solving.
>
>Let's say I have a class called A (Java syntax used for clarity):
>
>    public class A {
>    }
>
>And another called B, that is a subclass of A:
>
>    public class B extends A {
>        public Value foo;
>        public Value bar;
>    }
>
>There will be lots of other subclasses of A as well (let's call them C,
>D,
>E,
>etc), some of which will have a field called foo, and some of which
>won't.
>The
>class A will never have any fields -- its sole purpose is to be the
>base
>class
>of everything else.
>
>I have been able to successfully use a static bootstrap method in B, so
>that I
>can compile a call to invokedynamic on the imaginary method get_foo()
>of an
>instance of B, and then reroute the call inside B's bootstrap method
>via
>MethodHandles.Lookup.findGetter(), and finally return the current value
>of
>foo.
>So far, so good.
>
>However, at the place where I am compiling the invokedynamic
>instruction, I
>have no idea if the target is a B, C, D, or what.  All I know is that
>it
>must
>be an A.
>
>So what I really want to be able to do (I think) is to use a static
>bootstrap
>method in A. I want get_foo() to succeed for every invokedynamic call
>to an
>instance of A who's *subclass* really does have a field called foo.
>
>Unfortunately there doesn't seem to be a way to make A do what I want.
>I
>understand why that is -- foo doesn't exist in A, so there is no way to
>create
>a findGetter() call.  But I'm hoping there might be some clever way to
>do it
>anyway.  I've tried all kinds of different approaches (making yet
>another
>invokedynamic call from inside A, etc, etc) but I can't come up with
>anything
>that works.
>
>Any ideas?
>
>By the way, I've figured out how to do this the "old" way, by
>generating
>interfaces for each class that has e.g. a foo field, and casting to
>that
>interface every time I compile a get_foo() invocation.  This works, and
>its
>reasonably performant, but using invokedynamic seems like it would be a
>more
>elegant and flexible solution.
>
>
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>
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