Primer also provides a header so that you can push std::function objects directly to lua.

The idea is that it takes the signature R(Args...) from the std::function type, and puts that signature through PRIMER_ADAPT. The std::function object itself is stored in userdata as an upvalue to a closure, and the extracted arguments are passed to it when it is invoked.

Example Usage:

std::function<primer::result(lua_State * L, int x, int y)> f =
  [](lua_State * L, int x, int y) -> primer::result {
  if (y == x) { return primer::error{"bad input"}; }
  lua_pushinteger(L, x - y);
  return 1;
};

primer::push_std_function(L, std::move(f));

	Note
	std::function is somewhat at odds with the design goals of primer. It involves type erasure and extra dynamic allocations, and there's no obvious way to serialize a std::function, so we don't even try. We only provide this feature for convenience in a pure lua (not eris) application.

	Caution
	The std::function must not throw any exceptions when it is called, or std::terminate will be called.