How to print boost::any to a stream?

Question

I have a Map std::map, which comes from the boost::program_options package. Now I would like to print the content o

Answer 1

Define some aux function to output to stream:

template
bool out_to_stream(std::ostream& os, const boost::any& any_value)
{
    try {
        T v = boost::any_cast(any_value);
        os << v;
        return true;
    } catch(boost:: bad_any_cast& e) {
        return false;
    }
}

You can define a special formatting for some types

template<>
bool out_to_stream(std::ostream& os, const boost::any& any_value)
{
    try {
        std::string v(std::move(boost::any_cast(any_value)));
        os << "'" << v << "'";
        return true;
    } catch(boost:: bad_any_cast& e) {
        return false;
    }
}

or

template<>
bool out_to_stream(std::ostream& os, const boost::any& any_value)
{
    try {
        os << ((boost::any_cast(any_value))? "yes" : "no");
        return true;
    } catch(boost:: bad_any_cast& e) {
        return false;
    }
}

Then define an output operator for boost::any where you list all types you want to try to cast and output

std::ostream& operator<<(std::ostream& os, const boost::any& any_value)
{
    //list all types you want to try
    if(!out_to_stream(os, any_value))
    if(!out_to_stream(os, any_value))
    if(!out_to_stream(os, any_value))
    if(!out_to_stream(os, any_value))
        os<<"{unknown}"; // all cast are failed, an unknown type of any
    return os;
}

And then for a value_type:

std::ostream& operator<<(std::ostream& os, const boost::program_options::variable_value& cmdline_val)
{
    if(cmdline_val.empty()){
        os << "";
    } else {
        os<