std.algorithm.fill only accepts ForwardRange which is too restrictive. Both versions of fill should accept an InputRange.
A pull request is pending for this issue https://github.com/D-Programming-Language/phobos/pull/588
Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/e9dd66f8a0da1f4987a366f1a194b983c45c4b72 Issue 8112 - std.algorithm.fill accepts InputRange https://github.com/D-Programming-Language/phobos/commit/b1e1fa658db1a277b37c32b1e4568b18c8bdf441 Merge pull request #588 from gchatelet/input_range_fill_algorithm Issue 8112 - std.algorithm.fill must accept InputRange