Proposed API for JEP 259: Stack-Walking API

[Remi Forax]

----- Mail original -----
> De: "Paul Sandoz" <paul.sandoz at oracle.com>
> Cc: core-libs-dev at openjdk.java.net
> Envoyé: Mercredi 4 Novembre 2015 10:57:41
> Objet: Re: Proposed API for JEP 259: Stack-Walking API
> 
> 
> > On 4 Nov 2015, at 10:03, Remi Forax <forax at univ-mlv.fr> wrote:
> > 
> > Hi Paul,
> > 
> > The use of BaseStream was just an example, here is another one that works
> > only if the function first parameter type is declared as '? super
> > Stream<StackWalker.StackFrame>'.
> > 
> > static Function<Stream<?>, Integer> counter() {
> >  return stream::count;
> > }
> > 
> > ...
> > StackWalker walker = ...
> > int count = walker.walk(counter());
> > 
> 
> 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.

> 
> Paul.
> 

Rémi

[1] http://openjdk.java.net/jeps/8043488