Re: [Boost-users] [tuple] How to manipulate the types

From: Adrián Etchevarne (aetcheva_at_[hidden])
Date: 2006-05-30 11:00:34

David Abrahams wrote:

> 
> That's a lot easier to solve, in some sense, than the "Problem:"
> 
> above.  The cons list *is* a valid tuple.  So to inserta  new type at
> 
> the front, just write
> 
> 
> 
>     const<T, the-shorter-cons-list>
> 
> 
> 
Thanks to David and Joaquín for their response. 

tuple inherit from cons, so tuple is a cons.

cons<>  has an implicit conversion to tuple, but the types are not the same
(or I am missing something):

template< typename Cons, typename T>
struct p_front
{
        typedef cons<T, Cons> type;
};

typedef p_front< tuple<int>::inherited, float>::type pushed;

(is_same< pushed, tuple<float, int> >::value == false) // Not the same

If I declare

pushed value;

value has cons operations, not tuple operations. The implicit conversion
mitigates this. How I can sinthesize a tuple type? Joaquín's brute force
approach is the ultimate solution?

> You might also want to look at
> 
>
http://spirit.sourceforge.net/dl_more/fusion_v2/libs/fusion/doc/html/index.html
> 
> which was recently accepted into Boost.
> 
I will read it, thanks. It looks great!

Thanks,
        Adrián