Re: [boost] Re: [variant, MPL] Is there a variant -> mpl sequence metafunction ?

From: Jaakko Järvi (jarvi_at_[hidden])
Date: 2005-05-17 23:07:39

On May 17, 2005, at 10:22 PM, Larry Evans wrote:

> On 05/17/2005 10:07 PM, Jaakko Järvi wrote:
>> make_variant_over<Seq>::type
>> creates a variant type from an MPL Sequence.
>> Is there an operation that would do the opposite, create an MPL  
>> sequence from a variant?
>> I cannot just use the type parameter list as such because the types  
>> that stand for an empty
>> type are different in both libraries: boost::detail::variant::void_  
>> in variant, and something
>> else in MPL.
> I'd suggest making variant part of mpl.  With that, the problem
> disappears.

Yes, variant, mpl, tuple (or fusion), should play well together.
A good first step would be to start using the same type to mark that
no type was specified (instead of the variations void_, null_t, ...).

> Also, variant and tuple are duals of each other, in
> category theory terms; hence, it would make sense if the  
> implementations
> reflected this duality.  The code at:
>
> http://cvs.sourceforge.net/viewcvs.py/boost-sandbox/boost-sandbox/ 
> boost/indexed_set/?hideattic=0
>
> is an intial attempt at exploiting this duality.
>
Interesting, I must delay examining this until later, but for now,  
please note that
current tuple code base will be replaced with Fusion, hopefully in 1.34.

   Best, Jaakko

-- Jaakko Järvi, jarvi_at_[hidden]