In fact, <T> T walk(Function<Stream<StackFrame>, T> function, …) - without ?
extends T change,
You can do:
Function<Stream<StackWalker.StackFrame>, String> funct;
CharSequence chars = sw.walk(funct, i -> i);
I think it’s right to declare the return type of the function is "? extends T”.
Mandy
> On Oct 31, 2015, at 5:01 PM, Timo Kinnunen <timo.kinnu...@gmail.com> wrote:
>
> Hi,
>
> Regarding “
> I was pondering it and that’s why not changed in the last update. I agree
> with the upper bounded wildcard "? extends T” for the return type of the
> function.
> “
>
> How does changing the type from “T” to “? extends T” aid the method caller in
> any way? If the caller has a Function like this:
>
> Function<Stream<StackWalker.StackFrame>, String> funct;
>
> but they wished they could have walk use T=CharSequence instead, then they
> can simply assign the value returned from walk to a CharSequence variable:
>
> String result = sw.walk(funct, i -> i);
> CharSequence chars = result;
>
>
> Isn’t “? extends T” pointless here?
>
>
>
>
>
> Sent from Mail for Windows 10
>
>
>
> From: Mandy Chung
> Sent: Saturday, October 31, 2015 23:59
> To: Remi Forax
> Cc: core-libs-dev@openjdk.java.net
> Subject: Re: Proposed API for JEP 259: Stack-Walking API
>
>
>
> > On Oct 31, 2015, at 11:29 AM, Remi Forax <fo...@univ-mlv.fr> wrote:
> >
> > Hi Mandy,
> > I've crawled the code and the documentation again.
> >
> > In the doc and in the code, a lambda with one parameter doesn't require
> > parenthesis around the parameter,
> > (s) -> s.doSomething()
> > should be
> > s -> s.doSomething().
> >
>
> Oh right. (It didn’t look right to me but didn’t pay attention to it).
>
> >
> > In the doc of StackWalker,
> > in the first example, the local variable 'frame' should be named
> > ‘callerClass'
> >
>
> Fixed
> >
> > In the doc of getCallerClass(),
> > the first example do a skip(2) which i believe is not necessary anymore,
>
> It has to skip two frames. Use the second example, the stack looks like this:
>
> StackWalk::getCallerClass
> Util::getResourceBundle
> Foo::init
> :
> :
>
> > also instead of Optional.orElse, orElseGet is better because it avoids to
> > evaluate
> > Thread.currentThread().getClass() if not necessary.
> >
> > So the example should be:
> > walk(s -> s.map(StackFrame::getDeclaringClass)
> > .findFirst()).orElseGet(() ->
> > Thread.currentThread().getClass());
> >
>
> This would return Util.class instead of Foo.class
>
> > In the second example, the field walker should be declared 'final’.
>
> Sure. Fixed.
>
> >
> > And as i said earlier, the signature of walk() is:
> > <T> T walk(Function<? super Stream<StackWalker.StackFrame>, ? extends T>
> > function, IntUnaryOperator batchSizeMapper)
> >
>
> I was pondering it and that’s why not changed in the last update. I agree
> with the upper bounded wildcard "? extends T” for the return type of the
> function.
>
> But for the function’s input argument, can you help me understand why it
> should take "? super Stream<StackWalker.StackFrame>”? Is it useful to have
> function accepting supertype of Stream<StackFrame> rather than
> Stream<StackFrame>? VM should be the only source producing this StackFrame
> stream.
>
> On the other hand, I wonder if the stream argument should be Stream<? extends
> StackFrame> that may allow future implementation change.
>
> <T> T walk(Function<Stream<? extends StackWalker.StackFrame>, ? extends T>
> function, …)
>
> Mandy
