as_function¶

make sure an object is pushed as a function

template <typename Sig = sol::function_sig<>, typename... Args>
function_argumants<Sig, Args...> as_function ( Args&& ... );

This function serves the purpose of ensuring that a callable struct (like a lambda) can be passed to the set( key, value ) calls on sol::table and be treated like a function binding instead of a userdata. It is recommended that one uses the sol::table::set_function call instead, but if for some reason one must use set, then as_function can help ensure a callable struct is handled like a lambda / callable, and not as just a userdata structure.

This class can also make it so usertypes bind variable types as functions to for usertype bindings.

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#define SOL_ALL_SAFETIES_ON 1
#include <sol/sol.hpp>

int main () {
	struct callable {
		int operator()( int a, bool b ) {
			return a + (b ? 10 : 20);
		}
	};


	sol::state lua;
	// Binds struct as userdata
	// can still be callable, but beware
	// caveats
	lua.set( "not_func", callable() );
	// Binds struct as function
	lua.set( "func", sol::as_function( callable() ) );
	// equivalent: lua.set_function( "func", callable() );
	// equivalent: lua["func"] = callable();
}

Note that if you actually want a userdata, but you want it to be callable, you simply need to create a sol::table::new_usertype and then bind the "__call" metamethod (or just use sol::meta_function::call enumeration). This may or may not be done automatically for you, depending on whether or not the call operator is overloaded and such.

Here’s an example of binding a variable as a function to a usertype:

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#define SOL_ALL_SAFETIES_ON 1
#include <sol/sol.hpp>

int main () {
	class B {
	public:
		int bvar = 24;
	};

	sol::state lua;
	lua.open_libraries(sol::lib::base);
	lua.new_usertype<B>("B", 
		// bind as variable
		"b", &B::bvar,
		// bind as function
		"f", sol::as_function(&B::bvar)
	);

	B b;
	lua.set("b", &b);
	lua.script(R"(x = b:f()
		y = b.b
		assert(x == 24)
		assert(y == 24)
	)");

	return 0;
}