Consider: https://github.com/D-Programming-Language/phobos/blob/master/std/range/primitives.d#L152There is no explanation to it in the source code, and the line blames to https://github.com/D-Programming-Language/phobos/pull/2661 (irrelevant).
I've been wondering what that is myself, so I've just cargo-cult-copied it into my code. Thanks for the post.
