third-party/mapbox/variant_visitor.hpp

#ifndef MAPBOX_UTIL_VARIANT_VISITOR_HPP
#define MAPBOX_UTIL_VARIANT_VISITOR_HPP

#include <utility>

namespace mapbox {
namespace util {

template <typename... Fns>
struct visitor;

template <typename Fn>
struct visitor<Fn> : Fn
{
    using Fn::operator();

    template<typename T>
    visitor(T&& fn) : Fn(std::forward<T>(fn)) {}    
};

template <typename Fn, typename... Fns>
struct visitor<Fn, Fns...> : Fn, visitor<Fns...>
{
    using Fn::operator();
    using visitor<Fns...>::operator();

    template<typename T, typename... Ts>
    visitor(T&& fn, Ts&&... fns)
        : Fn(std::forward<T>(fn))
        , visitor<Fns...>(std::forward<Ts>(fns)...) {}
};

template <typename... Fns>
visitor<typename std::decay<Fns>::type...> make_visitor(Fns&&... fns)
{
    return visitor<typename std::decay<Fns>::type...>
        (std::forward<Fns>(fns)...);
}
    
} // namespace util
} // namespace mapbox

#endif // MAPBOX_UTIL_VARIANT_VISITOR_HPP