Bug 10460 – std.algorithm: some of algorithms don't use 'auto ref' for front

The following should use 'auto ref': Until, SetDifference, SetSymmetricDifference, SetIntersection, SetUnion (sorry, I'm too lazy to make a pull request...)

SetIntersection and SetUnion may be confusing to return auto ref since they contain overlap, e.g. int[] a = [1, 2, 3]; int[] b = [2, 3, 4]; foreach (ref e; setIntersection(a, b)) e = 0; Does this change the elements of 'a' or 'b'? For the difference ones, it makes sense because the element is only in one of the sets.

Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/5e0532b9e7d0a67567db0c7c9a3b541c829c75ed Fix Issue 10460 - auto ref for Union, SetDifference, SetSymmetricDifference https://issues.dlang.org/show_bug.cgi?id=10460 The rearrangement of SetSymmetricDifference.front was needed since auto ref doesn't deduce correctly when there are multiple return statements (by design), so a single return statement with the ternary operator was used. https://github.com/D-Programming-Language/phobos/commit/b61d9fa6844632ced1758f75ba2812c057d34bb8 Merge pull request #2461 from fb-pja/bug10460 Fix Issue 10460 - auto ref Union, SetDifference, SetSymmetricDifference