as_table

make sure an object is pushed as a table

template <typename T>
as_table_t {
        T& value() &;
        const T& value() & const;
        T&& value() &&;
};

template <typename T>
as_table_t<T> as_function ( T&& container );

This function serves the purpose of ensuring that an object is pushed – if possible – like a table into Lua. The container passed here can be a pointer, a reference, a std::reference_wrapper around a container, or just a plain container value. It must have a begin/end function, and if it has a std::pair<Key, Value> as its value_type, it will be pushed as a dictionary. Otherwise, it’s pushed as a sequence.

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

#include <vector>

int main(int, char*[]) {

	sol::state lua;
	lua.open_libraries();
	lua.set("my_table",
	     sol::as_table(std::vector<int> { 1, 2, 3, 4, 5 }));
	lua.script(
	     "for k, v in ipairs(my_table) do print(k, v) assert(k "
	     "== v) end");

	return 0;
}

Note that any caveats with Lua tables apply the moment it is serialized, and the data cannot be gotten out back out in C++ as a C++ type. You can deserialize the Lua table into something explicitly using the sol::as_table_t marker for your get and conversion operations using sol. At that point, the returned type is deserialized from a table, meaning you cannot reference any kind of C++ data directly as you do with regular userdata/usertypes. All C++ type information is lost upon serialization into Lua.

If you need this functionality with a member variable, use a property on a getter function that returns the result of sol::as_table.

This marker does NOT apply to usertypes.

You can also use this to nest types and retrieve tables within tables as shown by this example.

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

#include <vector>
#include <map>
#include <iostream>


}

// This second demo is equivalent to the first
// Nota bene the signature here
// Every container-type that's meant to be
// a table must be wrapped in `sol::as_table_t`
// it's verbose, so feel free to use typedefs to make it easy on
// you you can mix which parts are considered tables from Lua,
// and which parts are considered other kinds of types, such as
// userdata and the like
void demo_explicit(sol::as_table_t<std::map<std::string,
          sol::as_table_t<std::vector<std::string>>>>
          src) {
	std::cout << "demo, explicit sol::as_table_t<...>"
	          << std::endl;
	// Have to access the "source" member variable for
	// as_table_t
	const auto& listmap = src.value();
	SOL_ASSERT(listmap.size() == 2);
	for (const auto& kvp : listmap) {
		// Have to access the internal "source" for the inner
		// as_table_t, as well
		const std::vector<std::string>& strings
		     = kvp.second.value();
		SOL_ASSERT(strings.size() == 3);
		std::cout << "\t" << kvp.first << " = ";
		for (const auto& s : strings) {
			std::cout << "'" << s << "'"
			          << " ";
		}
	}
	std::cout << std::endl;
}

int main(int, char**) {
	std::cout << "=== containers retrieved from lua tables ==="
	          << std::endl;
	sol::state lua;
	// bind the function
	lua.set_function("f", &demo);
	lua.set_function("g", &demo_explicit);
	// Call it with a table that has string sequences set to
	// distinct keys
	lua.script(R"(
t = { 
	key1 = {'hello', 'there', 'world'},
	key2 = {'bark', 'borf', 'woof'}
}
f(t)
g(t)
	)");

	std::cout << std::endl;

	return 0;
}