Proposal: single-expression method bodies

Gavin Bierman gavin.bierman at
Mon Nov 27 10:25:20 UTC 2017

> On 25 Nov 2017, at 03:58, Daniel Trebbien <dtrebbien at> wrote:
> Hello Zheka,
> I personally like your idea of supporting expression lambda syntax with
> methods.  Being able to write simple getters as public int getSomeField()
> -> someField; would be very useful, in my opinion.


> I don't like the idea of expression lambda syntax support for switch cases,
> though, because I think that it wouldn't work well with fall-through
> support.  By way of example, consider:
> String s = switch (o) {
>    case Integer n:
>    case Double n:
>        return n.toString();
> }
> (I believe that reusing bound variable names like this is anticipated to be
> supported, but I could be wrong.)

I don’t think fall-through makes sense for expression switches. What you really want is an OR pattern, e.g. case P1, P1 -> e, which means “if it matches pattern P1 *or* pattern P2”. We have plans for this. Of course, the concrete syntax can be argued about… whatever is chosen will look a little odd to start with, but I would hope we’d get used to it fairly quickly.

Note also that OR patterns make sense even for conventional switch.


PS: Reusing variable names is surely useful, e.g. case Point(int x, 0), Point(int x, 1) -> …, but I think we need to be careful. Really what we are doing is introducing a new “x” in the body of the clause that is like a merge point of the two pattern occurrences. My personal preference is that the types should be identical, but one could imagine e.g. taking LUB of the types.

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