x eagerly intersected with y. TODO move to container_algorithm.d.
r-value and l-value intersection
alias K = uint; alias X = SSOHashMapOrSet!(K, void, null, FNV!(64, true)); auto x = X.withElements([12, 13].s); auto y = X.withElements([10, 12, 13, 15].s); y.intersectWith(x); assert(y.length == 2); assert(y.contains(12)); assert(y.contains(13));