recursive lambda as a local variable

[Gernot Neppert]

The line
Runnable r2 = this.r2::run;

from you examples shows one thing clearly: Bound Method References (BMRs)
are questionable at best, dangerous at worst.
Some quirky things about BMRs:

- The part left of the '::' can be an arbitrarily long expression that will
be evaluated immediately, while the method invocation itself will be
deferred until the corresponding SAM method is invoked. Thus, 'null' might
by bound now and detected much later.

- Due to the early binding/late execution issue, BMRs are confusingly
different from their plain lambda counterparts: 'this.r2::run' is very
different from '() -> this.r2.run()' because r2 might be assigned later.

- BMRs will usually neither save much typing nor be better readable than a
corresponding plain lambda expression.

Note that all of the above points are _not true_ with regards to Unbound
Method References, (e.g. String::valueOf or Pojo::getName), which I'd
consider a very useful addition to the lambda universe!

So, should we get rid of BMRs? ;-)




2013/9/11 Zhong Yu <zhong.j.yu at gmail.com>

> On Wed, Sep 11, 2013 at 12:36 PM, Dan Smith <daniel.smith at oracle.com>
> wrote:
> > I'm pretty sure that's just the way things work.
>
> > Fields can refer to themselves in their initializers;
>
>
> With lambda it is more confusing
>
> public class Tmp
> {
>     Runnable r1 = ()->r1.run(); // ok
>
>     Runnable r2 = this.r2::run; // compiles... but
> NullPointerException at runtime
> }
>
> Zhong Yu
>
>
>
>
> > local variables cannot.  (This is because fields always have a value
> (possibly null), while local variables can't be accessed before
> initialization.)
> >
> > You could try the same thing with an int:
> >
> > int i = i+1;
> >
> > —Dan
> >
> > On Sep 11, 2013, at 10:37 AM, Zhong Yu <zhong.j.yu at gmail.com> wrote:
> >
> >> This compiles: (b106)
> >>
> >>    class Test
> >>    {
> >>        Runnable r = ()->r.run();
> >>    }
> >>
> >> but this doesn't:
> >>
> >>    void test()
> >>    {
> >>        Runnable r = ()->r.run();
> >>    }
> >>
> >> is that intentional or a bug?
> >>
> >> Zhong Yu
> >>
> >
>
>