> On Nov 4, 2015, at 5:00 AM, Remi Forax <[email protected]> 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.
Mandy
