On Jan 4, 2019, at 6:07 AM, Tagir Valeev <amae...@gmail.com> wrote:
>
> For the record: I heavily support this. If then-branch cannot complete
> normally, then unwrapping the else-branch should preserve the program
> semantics. It works today, and it should work in future Java as well.
I agree also. But it is uncomfortable that the binding of the flow-scoped
variable gets buried in a place that is harder to spot.
Here's a possible compromise: Allow flow-scoped variables to leak
out the bottom of a statement, but only if they are predeclared before
the statement, in the parent block. They would be predeclared blank.
Example:
preconditions();
if (mist() && shadow() && !(x instanceof String s))
throw q;
else {
manyLinesOfStuff();
println(s); // s obscured by mist and shadow
}
<==>
preconditions();
String s;
if (mist() && shadow() && !(x instanceof String s))
throw q;
manyLinesOfStuff();
println(s); // s obscured by mist and shadow
Since the original s is always DU and never DA, we could choose
to allow the flow-bound s to merge with it. The binding would
then be discoverable as a dominating declaration, before the "if".
In this compromise, the dominating declaration would have to
be introduced before an entire if/else chain containing flow-scoped
bindings that are to be passed outside of the chain. That seems
reasonable to me, as a compromise between conciseness and
ease of reading.
— John
