----- Mail original -----
> De: "Mandy Chung" <mandy.ch...@oracle.com>
> À: "Remi Forax" <fo...@univ-mlv.fr>
> Cc: "Paul Sandoz" <paul.san...@oracle.com>, core-libs-dev@openjdk.java.net
> Envoyé: Jeudi 5 Novembre 2015 22:48:45
> Objet: Re: Proposed API for JEP 259: Stack-Walking API
>
>
> > On Nov 4, 2015, at 5:00 AM, Remi Forax <fo...@univ-mlv.fr> wrote:
> >
> >>
> >> Good point. Damn, i don’t like wildcards :-)
> >>
> >> The following works fine:
> >>
> >> static <T> Function<Stream<T>, Long> counter() {
> >> return Stream::count;
> >> }
> >>
> >> But there could also cases where one is stuck using a wildcard:
> >>
> >> Function<Stream<?>, Long> f = Stream::count;
> >
> >
> > Wildcards are not that complex, but because they are use-side annotations,
> > it's really easy to forget them, and IDEs do not help here :(
> >
> > I really hope that the JEP about declaration site variance [1] will be
> > implemented at the beginning of jdk 10, it will remove the need of
> > wildcards for functional interfaces.
> >
>
> Remi, Paul,
>
> The current StackWalker::walk method:
> <T> T walk(Function<Stream<StackFrame>, T> function)
>
> This would mean that the StackWalker API is intended to work with a function
> taking Stream<StackFrame> but not Stream<?>.
>
> Changing to
> <T> T walk(Function<? super Stream<StackFrame>, ? extends T> function)
>
> will allow use of some existing functions taking Stream<?>. I don’t object
> changing it to use wildcard.
>
> However, the StackWalker API is specific for reading StackFrame and I would
> expect it’s reasonable if it doesn’t work with a function taking Stream<?>
> as the useful functions such as Stream::count,
> Stream::collect(Collectors.toList(…)) can be used.
>
> Just want to double confirm the advice which way to go.
yes, it is.
Stream<?> is perhaps not the best example, using a Function<? super
Stream<StackFrame>, ? extends T> also allow calls that use a Stream<Object> (no
wildcard here !),
like this:
Function<Stream<Object>, Void> fun = stream -> {
stream.forEach(System.out::println); return null; };
stackWalker.walk(fun);
>
> Mandy
regards,
Rémi
