::emplace

#include <new>
#include <type_traits>
#include <utility>

namespace details {

  template<typename Type>
  struct emplace_arg_t { };

  template<typename T, typename... Args>
  void emplace(emplace_arg_t<T>, void* location, Args&&... args)
  noexcept(std::is_nothrow_constructible<T, Args&&...>::value) {
    new (location) T(std::forward<Args>(args)...);
  }

  template<typename... Args>
  void emplace(emplace_arg_t<void>, void* location, Args&&... args)
  noexcept(noexcept(new (location) auto(std::forward<Args>(args)...))) {
    new (location) auto(std::forward<Args>(args)...);
  }

}

template<typename Type = void, typename... Args>
void emplace(void* location, Args&&... args)
noexcept(noexcept(details::emplace(details::emplace_arg_t<Type>{}, location, std::forward<Args>(args)...))) {
  details::emplace(details::emplace_arg_t<Type>{}, location, std::forward<Args>(args)...);
}