On Sat, Oct 13, 2012 at 10:33 PM, Matt Calabrese <rivorus@gmail.com> wrote:
On Sat, Oct 13, 2012 at 9:38 PM, Lorenzo Caminiti <lorcaminiti@gmail.com>wrote:
Because I don't know how to support the following:
template( typename(ObjectType) T, typename(MapType<T>) U ) concept_map (RandomAccessIterator) ( T* )
Where U is of constrained by MapType<U, T>. The only way I can think to do this is typename(MapType<mpl::_, T>) U (then it'd be up to Boost.Generic to deal with mpl::_ used this way). Does this use case apply to associated types?
This applies to using "auto" in the parameter list in N2914. While I don't support it yet, I was planning on doing it via the preprocessor rather than trying to do it with template metaprogramming,
This is also better because the pp parser can get all the "traits" of the declaration (instead than leaving the substitution of auto/mpl::_ to the back-end). This way different back-ends can do different things with the parsed pp "traits".
though I haven't thought about it in depth yet:
template( ((ObjectType)) T, (((MapType)( auto, T )) U)
It will have to be something like that, maybe with typename to distinguish from value template parameters as I mentioned before: template( typename(ObjectType) T, typename(MapType)(auto, T) U ) // (1) ... Or, as I was saying, can't we just require the use of requires ;) instead: template( typename T, typename U ) requires( ObjectType<T>, (MapType<U, T>) ) // (2) ... Does Boost.Generic need ObjectType and MapType separately (as per 1) or it can use their instantiations Object<T> and MapType<U, T> (as per 2)?
This corresponds to the N2914 syntax mentioned in [temp.param] on page 312 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2914.pdf
--Lorenzo