Every reviewer and contributor to this discussion is, of course, entitled to their view of: - What makes a library useful (including how many compilers are supported)? - What the standard for Boost libraries should be (minimum compiler support)? While it is may be beneficial to discuss those two questions above (perhaps even independent of Hana's review, for all of Boost, and with a different subject), I just want to make certain that nobody is under the impression that Hana is ineligible for review because of compiler support. Here is my take on it: 1. The current requirements for Boost libraries do advise authors of only:[1] a. "Aim for ISO Standard C++" b. "There is no requirement that a library run on C++ compilers which do not conform to the ISO standard." c. "There is no requirement that a library run on any particular C++ compiler. Boost contributors often try to ensure their libraries work with popular compilers." 2. Compiler vendors today are more actively trying to conform to the standard. In my mind it is a question of "when" g++ will support the necessary features, not "if". These aren't contentious things that anyone is concerned will never be supported. (e.g. It is not like we're back in 2003 and someone has submitted a library that is littered with unconditional use of the 'export' keyword). 3. Usefulness is more important that [current] compiler support. If [future] g++ 5.3 and clang 3.5 users get to enjoy useful libraries, these libraries can drive language conformance in other compiler vendors. (Useful and popular Boost libraries driving minimum C++ language feature support in compiler vendors is also an appealing thought). Glen [1] http://www.boost.org/development/requirements.html