My lambda leftovers

[Tagir Valeev]

Hello!

As for throw, I think it should just be converted to an expression,
probably of the same type as a null literal (thus throw statement will
become an expression statement). In this case it could be useful not
only in lambdas, like:

return list.isEmpty() ? throw new NoSuchElementException() : list.get(0);

I believe, it was discussed in context of pattern matching.

With best regards,
Tagir Valeev.

On Fri, Oct 6, 2017 at 6:16 PM, Remi Forax <forax at univ-mlv.fr> wrote:
> Hi all,
> The JEP 302 list some improvements but I think some are missing, obviously, it's up to debate :)
>
> So here is my list of left leftovers:
> - support throw statement as a lambda expression
>
>   I think we have already discussed informally about this one.
>   The compiler should allow to have a lambda expression that starts with throw.
>
>   so a code like this will become valid
>   merge(key, value, (_, _) -> throw new IllegalStateException("key " + key + " already present));
>
>
> - allow void to be converted to Void (by returning null)
>
>   This proposal is perhaps more controversial, currently there is no way to simply convert a lambda statement to a lambda expression.
>   So a code like will compile
>
>    <T, R> R sync(T initial, Function<? super T, ? extends R> fun) {
>     synchronized(lock) {
>       return fun.apply(initial);
>     }
>   }
>
>   Consumer<String> c = System.out::println;
>   sync("foo", c::accept);     // the compiler should generate a synthetic static method that returns null
>
>   This proposal is problematic because:
>   - it implicitly produces a null, which is a bad idea
>   - if there are several overloads, a lambda statement can now match more methods so the compiler may reject code that was previously working or worst call another method that the one that was originally selected.
>
>
>  The other question is should the conversion be extended to work with non lambda code,
>  i.e. consider that 'return' or an implcit 'return' can be trasformed to a return null by the compiler.
>
>   Void m() {
>     return;     // the compiler generates return null;
>   }
>
>   Void m() { }  // the compiler generates return null;
>
>
>  On the positive side, it mix well with the switch expression proposed in the Pattern Matching JEP.
>
>   Supplier<Void> supplier =
>       () -> switchexpr(someValue) {
>                 case 0 -> System.out.println("foo");
>                 default -> { /* empty */ }
>             };
>
>
> regards,
> Rémi
>
> [1] http://openjdk.java.net/jeps/302