Re: [boost] Re: Small tuple extension

From: Giovanni P. Deretta (lordshoo_at_[hidden])
Date: 2005-04-27 17:33:23

Sorry for the no-op email, I don't know how it did get sent.

Larry Evans wrote:
> 
> 
> OOPS.  Maybe you meant that although there were, e.g. 3 enumerators in
> the enumeration, the map was only defined for 2 or 1 or none.  To be 
> concrete, an example would be where enum_map<0> in the above vault code
> were:
> 
>   template
>   <
>   >
>   struct
> enum_map
>   < 0
>   >
> {
>       enum
>     field_names
>     { f_0
>     , f_1
>     , f_2
>     };
> 
>       template<field_names FieldName>
>       struct
>     field_name
>     {};
> 
>         typedef
>       mpl::map
>       < mpl::pair<field_name<f_0>, type_i<0> >
>       >
>     field_map
>     ;
> };
> 
> then I can see your point about "tuple might not map
> the whole enum set".
> 

Exactly, and this is something i need (and probably is the only reason 
to use some kind of tag instead of indexes).  In code that i wrote there 
were  a set of functions that had similar effects and had multiple 
return values (as tuples).  The return values weren't the same, but all 
of them had a common types.  Some generic code had to work with this 
functions and needed to extract this common types from the tuples.  A 
typed get was exactly what i needed.  Fusion 'find' would probably have 
done the job as well, but i did not know it untill now.

--
Giovanni P. Deretta
Giovanni P. Deretta