Why doesn't reduce() throw a Runtime exception on an empty stream instead of returning the identity?

Mike Simmons wrote:
With this method, how would you ever get a V instance at all?  You have a stream of T, and you have a BiFunction to take a V and a T, and return a V.  Which means you need at least one V to use that function.  That's why you need an identity V instance, to start the reduction off.  

Mike Simmons wrote:
And for parallel processing, each worker thread will use that same identity V instance to start off processing its own subset of elements, before combining later with the combiner.  And if any of those worker threads finds there are no elements for them to process (maybe it turns out that there's a filter() method that eliminates all the elements that might have been expected) you want the worker to not freak out and throw an exception, just return the identity value unmolested, so it can still be combined with the other results safely.

Paul Clapham wrote:Let's have a go at that with String Templates:
throw new RuntimeException(STR."""Stream required \{ min } elements, found only \{ a.count }.""");
I haven't tested this but I can see that the idea is still subject to futzing around to get the spaces in the right places.