Re: [boost] [review][mp11] Formal review of Mp11

Subject: Re: [boost] [review][mp11] Formal review of Mp11
From: Peter Dimov (lists_at_[hidden])
Date: 2017-07-17 11:05:02

> > We already have subnamespaces in std (e.g. std::chrono), so your 
> > standardization plan could be realized as s/boost/std.
>
> It could if I wanted to propose std::mp::if_, but I don't. I want to 
> propose std::mp_if.
>
> I know that this makes the library more difficult to use in other Boost 
> libraries where there's no convenient place to put the using directive. 
> :-/

To expand on this a bit:

There are, in general, two main modes of use of Mp11, serving two audiences. 
One is the "easy mode", where one includes <boost/mp11.hpp>, combines that 
with `using namespace boost::mp11;`, then goes ahead using mp_this and 
mp_that without qualification. This serves (a) people who play with 
metaprogramming in short test cases, (b) people who have a need for a 
metaprogram in a .cpp file (or an internal header file not meant for public 
consumption), whether library or application one.

Mode two is in use in header-only libraries. There the library author is 
generally reluctant to employ the using directive, which forces the 
comparatively awkward mp11::mp_this style.

I realize that my choice gives preference to case one at the expense of case 
two.