Question

I try to use the following example from boost:

#include <boost/container/map.hpp>
struct data
{
    std::string label;
    //A map holding still undefined 'data'
    boost::container::map<std::string, data> m_;
};

int main(int argc, char* argv[])
{
    data d,d1,d2;
    d.m_["hello"] = d1;
    return 0;
}

unfortunately it does not compile and I can’t figure why.

Compilers Message (just the end of it):
../../3d_party_4_5_8/boost_1_49_0/boost/container/detail/tree.hpp|183| error: no match for גoperator=ג in ג((boost::container::container_detail::rbtree_node, std::allocator >, data>, void*>*)this)->boost::container::container_detail::rbtree_node, std::allocator >, data>, void*>::m_data.boost::container::container_detail::pair, std::allocator >, data>::second = p->boost::container::container_detail::pair, std::allocator >, data>::secondג
Analyzer.cpp|139| note: candidates are: data& data::operator=(data&)

Answer 1

I think you are compiling in C++03 mode:
Please see Assignment operator in classes derived from or holding copyable and movable types. Your assignment operator is non-const as shown in the error message: data& data::operator=(data&), this is the problem. boost::container emulates move semantics in C++03 compilers, and in order to do this defines a non-const copy constructor. One possible solution is too add the following to data:

data& operator=(data x)
{
    std::swap(*this, x); 
    return *this;
}

or

data& operator=(const data& x)
{
    label = x.label 
    return *this;
}

depending on your needs.