Support multiple return values

[kunitoki]

Sometimes you might want to push multiple values for a type.

For example when pushing all values of a variant type or std::pair. Currently it's done by pushing them in a table.

But in my case I don't want a table to return, I want each value separately in Lua.

[[nodiscard]] static Result push(lua_State* L, Type const& e)
{
	// push a value
	// push another value
	Result r;
	r.num_args(2); // We pushed two values so set it to 2
	return r;
}

[kunitoki]

This means we might need to change Stack, but it's difficult to come up with a solution that could work without making thing super complicated and unflexible, especially if we push the burden of supporting both modes to the developer integrating its own types.

Also, if you need this from lua, you could use table.unpack like:

local array = {1, 2, 3, 4}
local a, b, c, d = table.unpack(array)

[rpatters1]

Is there some way to use std::tie or std::tuplet? I have often wished there was some way to have a C function return a std::tuplet (or pair) and have LB spin it out on the stack as separate return values. Maybe an option when the function is registered? Or a wrapper class that does the same?