myahya myahya - 4 months ago 35
C++ Question

Tuples of unknown size/parameter types

I need to create a map, from integers to sets of tuples, the tuples in a single set have the same size. The problem is that the size of a tuple and its parameter types can be determined at runtime, not compile time. I am imagining something like:

std::map<int, std::set<boost::tuple> >

but not exctly sure how to exactly do this, bossibly using pointers.

The purpose of this is to create temporary relations (tables), each with a unique identifier (key), maybe you have another approach.


The purpose of boost::tuple is to mix arbitrary types. If, as you say,

I am only inserting integers

then you should use map< int, set< vector< int > > >. (If I were you, I'd throw some typedefs at that.)

To answer the original question, though, boost::tuple doesn't allow arbitrary types at runtime. boost::any does. However, any does not support comparison so there's a little more work if you want to use it in a set.

typedef vector< boost::any > tuple;
struct compare_tuple { bool operator()( tuple const &l, tuple const &r ) const {
    assert ( l.size() == r.size() );

    for ( tuple::iterator lit = l.begin(), rit = r.begin();
          lit != l.end(); ++ lit, ++ rit ) {
        assert ( lit->type() == rit->type() );

        if ( lit->type() == typeid( foo ) ) { // find the type and perform "<"
            return boost::any_cast<foo>(*lit) < boost::any_cast<foo>(*rit);
        } else if ( lit->type() == typeid( bar ) ) {
            return boost::any_cast<bar>(*lit) < boost::any_cast<bar>(*rit);
        } /* etc; you will need to enumerate all the types you can insert */
} };

typedef std::map< int, std::set< tuple, compare_tuple > > main_map;