mapbox::variant pattern matching

variant.h

#include "variant/variant.hpp"
template<typename ...T> using variant = mapbox::util::variant<T...>;

namespace matchdetail {
  template<typename C, typename Arg>
  Arg lambda_argument(void(C::*)(const Arg&) const) {}

  template<typename Other>
  void lambda_argument(Other) {}

  template<typename Var, typename Fn>
  void run_if_match(const Var& var, const Fn& code) {
    typedef decltype(lambda_argument(&Fn::operator())) T;
    static_assert(!std::is_void<T>::value, "match() lambda must take const T&");
    if (var.template is<T>()) {
      T m = var.template get<T>();
      code(m);
    }
  }
}

/* Usage:

   variant<A, B, C> obj;
   match(obj,
         [&](const A& a) {
            ...
         },
         [&](const C& c) {
            ...
         }
        );
*/

template<typename Var>
void match(const Var&) {}

template<typename Var, typename First, typename ...Rest>
void match(const Var& var, First first, Rest... rest) {
  matchdetail::run_if_match(var, first);
  match(var, rest...);
}

Note that this is pretty much obsolete now that mapbox has a match() function.