Future.resultNow / exceptionNow

[Brian Goetz]

That would kind of defeat the purpose.  If you follow the discipline of 
structured concurrency, where the parent always waits for the child to 
complete (StructuredExecutor offers methods and patterns for 
guaranteeing this), then you will know with confidence that the future 
is complete, and it is safe to just ask for the result. Throwing ISE 
means you made a coding error (i.e., you forgot to wait for the 
children), like dereferencing an object reference without knowing it was 
non-null, indexing into an array without knowing the bounds, or calling 
Optional::get without knowing the Optional holds a value.

Catching ISE here would be like blindly wrapping every dereference with 
"catch NPE", or every array access with "catch AIOOBE".



On 11/20/2021 11:43 AM, Alex Otenko wrote:
> Is there a strong opinion about Future.resultNow and exceptionNow throwing
> IllegalStateException? It seems there will likely be boilerplate
> try-catching, as there is no safe way to inquire in what way the Future is
> isDone.
>
> Returning Optional seems a nicer alternative.
>
> Alex