Ruby Issue Tracking System

08/14/2026

03:41 PM Ruby Feature #22245 (Open): Reduce Array#& cost when self is much shorter than the argument

# Abstract
For intersections of larger arrays, Ruby builds a temporary hash from the argument to `Array#&`. As a result, `short & long` can be slower and use much more temporary memory than `long & short`. Callers cannot always choose... andrey.samsonov@gmail.com (Andrey Samsonov)

08/10/2020

12:27 PM Ruby Feature #17109: Eliminate the performance impact of operands' order in array's | and &

> > The order is preserved from the original array.
My bad, I missed the comment. In this case, I think the optimisation is not worth a change in the spec. andrey.samsonov@gmail.com (Andrey Samsonov)

08/09/2020

09:52 PM Ruby Feature #17109 (Rejected): Eliminate the performance impact of operands' order in array's | and &

When I do intersection (`a & b`) or union (`a | b`), usually the array in one position is more likely longer than the one in the other position. I always try to remember in what order I should write `a` and` b` for the best performance. ... andrey.samsonov@gmail.com (Andrey Samsonov)