#include <boost/signals2/signal.hpp>
#include <cassert>

struct moveonly_data
{
    moveonly_data(int data) : m_data(data){}
    moveonly_data(moveonly_data&&) = default;

    // The assignment operator should not be required here
    moveonly_data& operator=(moveonly_data&&) = default;

    moveonly_data(const moveonly_data&) = delete;
    moveonly_data& operator=(const moveonly_data&) = delete;
    int m_data;
};

moveonly_data moveonly_return_callback(int val)
{
    return {val+1};
}

int main()
{
    boost::signals2::signal<moveonly_data(int)> sig;
    sig.connect(moveonly_return_callback);
    int data{3};
    auto ret = sig(data);
    assert(ret->m_data == 4);
}