Re: [boost] [GSoC] [Boost.Hana] Formal review request

30 Jul 2014


      Louis Dionne  writes:
...
pfultz2  writes:
[...]
...
...
There are two things here. First, the decision not to split the library
into
a thousand headers was considered a feature, because it meant that you did
not need to include countless headers to get some functionality. Since the
library is very lightweight, it does not cause a compile-time performance
problem to include the whole list.hpp header.
Even so, in your implementation of list.hpp, it may not be performance hit
to include it together, but perhaps as a user, I could be adapting a type 
where each of those methods are heavyweight, so I would want to seperate 
them out into seperate headers.
Ahhh, now I understand what you mean. I think that's possible and I'll 
reply when I'm fixed. Basically, I'll try to split the adaptor for Fusion
into separate header and see if it works.
Ok, I tried it in a sandbox and here's what you could do:
    
    // In some forward declaration header.
    template <>
    struct Foldable::instance<YourDatatype> : Foldable::mcd {
        template 
        static constexpr auto foldl_impl(F f, State s, Xs xs);

        // other forward declarations ...
    };

    // In some header holding the actual implementation of foldl.
    template 
    constexpr auto Foldable::instance<YourDatatype>::
                   foldl_impl(F f, State s, Xs xs) 
    { 
        // ...
    }


Regards,
Louis