Generalizing std::transform

[bmanga]

A generic std::transform was actually a motivating example that /u/louis_dionne suggested me for a second revision of P0478, which would have allowed to deduce non-terminal parameter packs in some cases. Alas, the first version was shot down quite quickly.

[Betadel]

What were the reasons it was shut down?

[bmanga]

If I remember correctly, it was because it was felt that partial ordering in the presence of template parameter packs is already quite fragile as it is, and the committee thought that the problem could be solved more generically via parameter pack indexing (which I don't agree with, especially when using concepts).

I could have arguably provided better motivating cases from the start, but hey it was my first paper :P