How can I create a boost tuple which depends on the typename of tuple?

I'd like to create tuple of type which depends on the name of that type.

Maybe example would clarify my problem:

//T would be boost::tuples::tuple<int, int, ...>
template <typename T>
T generate()
{
    typedef T GT;
    typedef boost::tuples::element<0,GT>::type tt0;
    typedef boost::tuples::element<1,GT>::type tt1;
    typedef boost::tuples::element<2,GT>::type tt2;
    if(tt3==null_type)
        return boost::tuples::make_tuple<tt0,tt1>(static_cast<tt0>(1), static_cast<tt1>(2));
    else
        return boost::tuples::make_tuple<tt0, tt1, tt2>(static_cast<tt0>(1), static_cast<tt1>(2), ...);
}

EDIT: I've found nice way, template recursion. Prob开发者_如何学编程lem solved.

typedef typename oost::tuples::element<0,GT>::type tt0;

...

if(tt3==null_type) 

you cant check types likes this, use mpl::if_ instead

        return boost::tuples::make_tuple<tt0,tt1>(static_cast<tt0>(1), static_cast<tt1>(2));
    else
        return boost::tuples::make_tuple<tt0, tt1, tt2>(static_cast<tt0>(1), static_cast<tt1>(2), ...);

are you trying to remove null_type? Just use boost::fusion::remove.

Here is another solution:

template <typename T>
tuple<tt0,tt1> 
generate(typename enable_if<is_same<tt3, null_type> >::type* = 0) {
    typedef typename boost::tuples::element<0,T>::type tt0;
    typedef typename boost::tuples::element<1,T>::type tt1;
     return make_tuple(tt0(1), tt1(1));
}

similary for other case.

notice: boost::enable_if, boost::is_same