Stream optimization checks

[schlosna]

What happened?

Code like stream.map(foo::expensiveConversion).limit(N), stream.sorted().limit(N), or stream.filter(this::someFilter).sorted() does not trigger any warnings for inefficiency.

What did you want to happen?

If one writes code that limits or filters a Stream we should push those predicates earlier in the pipeline where possible to limit the amount of downstream computation and allocations are performed.

[jdm2212]

this is fine:

stream.map(foo::expensiveConversion).limit(N)

this is not fine:

stream.sorted().limit(N)

the latter has a step that needs to touch all elements in the stream (sorted()) whereas the former does not

[jdm2212]

it is also entirely correct in many cases to do stream.sorted().limit(N) if you just want the top N elements of the stream, sorted by some property

it's only dangerous if you erroneously believe that the limit will be applied to the unsorted stream and bound the number of items being sorted