Boost Fusion: convert adapted struct type to text

Question

Given a struct like this:

struct Foo
{
    int x;
    int y;
    double z;
};

BOOST_FUSION_ADAPT_STRUCT(Foo, x, y, z);       

I want to generate a string like this:

"{ int x; int y; double z; }"

I have seen how to print the values of a Fusion adapted struct, but here I need to print the types and names only.

How can I do this mostly simply? I'm not married to Boost.Fusion if there's a better way.

Answer 1

I think you can get something similar to what you want by making some slight modifications on the code in this answer. You can easily get the member name using boost::fusion::extension::struct_member_name but, as far as I know, you can't directly get the member type name. You can get the member type using boost::fusion::result_of::value_at (amongst other options) and I've chosen to use Boost.TypeIndex to get its name (in varying degrees of prettiness, depending on the compiler and the types in question). All of this is assuming that you actually need the Fusion adaptation, if you don't you can probably get a simpler approach that does only what you need.

Full Code
Running on WandBox (gcc)
Running on rextester (vc)

#include <iostream>
#include <string>

#include <boost/mpl/range_c.hpp>
#include <boost/fusion/include/for_each.hpp>
#include <boost/fusion/include/zip.hpp>
#include <boost/fusion/include/at_c.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/mpl.hpp>

#include <boost/type_index.hpp>


namespace fusion=boost::fusion;
namespace mpl=boost::mpl;

struct Foo
{
    int x;
    int y;
    double z;
};

BOOST_FUSION_ADAPT_STRUCT(Foo, x, y, z);

struct Bar
{
    std::pair<int,int> p;
    std::string s;
};

BOOST_FUSION_ADAPT_STRUCT(Bar, p, s);

template <typename Sequence>
struct Struct_member_printer
{
    Struct_member_printer(const Sequence& seq):seq_(seq){}
    const Sequence& seq_;
    template <typename Index>
    void operator() (Index) const
    {

        std::string member_type = boost::typeindex::type_id<typename fusion::result_of::value_at<Sequence,Index>::type >().pretty_name() ;
        std::string member_name = fusion::extension::struct_member_name<Sequence,Index::value>::call();

        std::cout << member_type << " " << member_name << "; ";
    }
};
template<typename Sequence>
void print_struct(Sequence const& v)
{
    typedef mpl::range_c<unsigned, 0, fusion::result_of::size<Sequence>::value > Indices; 
    std::cout << "{ ";
    fusion::for_each(Indices(), Struct_member_printer<Sequence>(v));
    std::cout << "}\n";
}

int main()
{
    Foo foo;
    print_struct(foo);

    Bar bar;
    print_struct(bar);
}