Edward Diener
[...]
Numerous Boost libraries currently use MPL. If you want to have Hana as a Boost library, if it is accepted after review, I think you will have to get used to the idea that Boost will have more than one metaprogramming library. If Hana proves popular enough with metaprogrammers they will switch away from MPL to Hana.
I do not know what you mean by "two metaprogramming libraries living side by side" but I believe that two libraries whose purposes are similar but whose programming interfaces are different is never a detriment to Boost as long as both are quality libraries which other programmers find useful.
I apologize; what I said was unclear. I did not mean that the MPL (or Fusion for that matter) should go away. I also do not expect people to port old code from MPL/Fusion to Hana, except in some rare cases. Actually, Hana even provides interoperation with MPL and Fusion, so I do recognize the importance of these libraries. What I meant is that I think we should strive for a unified treatment of metaprogramming in the long term. Hence, I would hope that _new_ libraries are written against Hana instead of MPL/Fusion, of course if those libraries are meant to be used on modern compilers. As for "two metaprogramming libraries living side by side", I meant that working on a _new_ C++11/14 type-only MPL is a bad idea IMO, because Hana is a strict superset of such a type-level only library. Of course, this is my biased opinion, and it is why I switched from MPL11 to Hana; I thought it was more promising. However, I have absolutely nothing bad to say about a revamping of the current MPL in a backward compatible way, except that it might be hard (but not impossible) to achieve without breaking some code. Actually, if someone is interested in attempting a backward compatible MPL, I could probably provide a good part of the code by just looking at an older snapshot of the MPL11, before backward compatibility was broken. Louis