Typedef'ing basic_ptree from Boost - c++

Question

I'm using Boost.PropertyTree for a project and I want to use user-defined types for Key and Data instead of the std::string that Boost uses in the ptree typedef.
However when I typedef basic_ptree myself I get the following compiler errors:
1> main.cpp
1>c:\boost_1_49_0\boost\property_tree\ptree.hpp(82): error C2027: use of undefined type 'boost::property_tree::path_of<Key>'
1> with
1> [
1> Key=int
1> ]
1> c:\users\mathias\documents\visual studio 2012\projects\testappern\testappern\main.cpp(10) : see reference to class template instantiation 'boost::property_tree::basic_ptree<Key,Data>' being compiled
1> with
1> [
1> Key=int,
1> Data=int
1> ]
1>c:\users\mathias\documents\visual studio 2012\projects\testappern\testappern\main.cpp(13): error C2664: 'boost::property_tree::basic_ptree<Key,Data>::add_child' : cannot convert parameter 1 from 'int' to 'const boost::type &'
1> with
1> [
1> Key=int,
1> Data=int
1> ]
1> Reason: cannot convert from 'int' to 'const boost::type'
1> The target type has no constructors
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
The following snippet shows and example how I typedef basic_tree and get the compiler errors:
#include <iostream>
#include <boost\property_tree\ptree.hpp>
using namespace boost::property_tree;
typedef basic_ptree<int, int> IntTree;
int main(int argc, char* argv[])
{
IntTree tree;
IntTree child;
int index = 42;
tree.add_child(index, child);
return 0;
}
So my question is, how do I typedef it correctly?
If it's any interest I'm running MSVC 2012.
Thanks in advance!

Answer 1

According to the contents of boost/property_tree/ptree_fwd.hpp, if you want to use a custom type as a key, you should follow this:
/// If you want to use a custom key type, specialize this struct for it
/// and give it a 'type' typedef that specifies your path type. The path
/// type must conform to the Path concept described in the documentation.
/// This is already specialized for std::basic_string.
So you can not simply use int. Refer to the documentation for more information, as the code says.

Answer 2

Here is an example of basic_ptree <int, int>
//path class must conform Path concept
template<> class boost::property_tree::path_of < int >
{
public:
typedef int key_type;
typedef boost::property_tree::path_of < int > type;
boost::property_tree::path_of<int>(vector<int>& vals)
{
std::transform(vals.begin(), vals.end(), back_inserter(_impl),
[&](int v) -> int{ return v; });
}
key_type reduce()
{
key_type res = *_impl.begin();
_impl.pop_front();
return res;
}
bool empty() const
{
return _impl.empty();
}
bool single() const
{
return _impl.size() == 1;
}
std::string dump() const
{
std::string res;
std::for_each(_impl.begin(),
_impl.end(), [&res](key_type k) -> void
{
res.append(".");
res.append(boost::lexical_cast<std::string>(k));
});
return res;
}
private:
deque<key_type> _impl;
};
//usage:
typedef boost::property_tree::basic_ptree < int, int> custom_int_tree_t
//or
typedef boost::property_tree::basic_ptree < int, void*> custom_int_tree2_t