Re: The boost.variant library and boost::make_recursive_variant

From:

dasjotre <dasjotre@googlemail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 06 Jul 2007 03:25:20 -0700

Message-ID:

<1183717520.346426.161540@w3g2000hsg.googlegroups.com>

On 5 Jul, 02:49, Miros aw Makowiecki <miroslaw.makowie...@gmail.com>
wrote:

We have this code:
typedef boost::make_recursive_variant<
      int
    , std::vector< boost::recursive_variant_ >
    >::type int_tree_t;
Use of the resultant variant type is as expected:
std::vector< int_tree_t > subresult;
subresult.push_back(3);
subresult.push_back(5);

std::vector< int_tree_t > result;
result.push_back(1);
result.push_back(subresult);
result.push_back(7);

int_tree_t var(result);
According to documentation in library of boost.variant, a variable var
it's ( 1 ( 3 5 ) 7 ).
Queastion:Who do it print in language C++ by next of std::cout?
  Thanks in advance.

On 5 Jul, 02:49, Miros aw Makowiecki <miroslaw.makowie...@gmail.com>
wrote:

(I suppose the question is HOW to print var to get ( 1 ( 3 5 ) 7 ) )

you provide visitor with function operator overloaded for all
the types your variant can hold.

struct print_visitor : public boost::static_visitor<void>
{
        // print int
    void operator()(int i) const
    {
        std::cout << i << ' ';
    }
        // print vector of int_tree_t
    void operator()(std::vector<int_tree_t> const & v) const
    {
        std::cout << " ( ";
        for(std::size_t i=0; i<v.size(); ++i )
            boost::apply_visitor(print_visitor(), v[i]);

        std::cout << " ) ";
    }
};

boost::apply_visitor(print_visitor(), var);

regards

DS