#include <map>
#include <memory>
using namespace std;

typedef int AssetId;
struct Material {
    int _id;
    Material(int id) : _id(id) {}
    int AssetId() const { return _id; }
};
typedef std::map< AssetId, std::shared_ptr<Material> > MaterialsMap;    

MaterialsMap  m_materials;

int main() {
    std::shared_ptr<Material> pMaterial(new Material(42));
    m_materials.insert( MaterialsMap::value_type(pMaterial->AssetId(), pMaterial) );
}