sol2/examples/usertype.cpp

#define SOL_CHECK_ARGUMENTS
#include <sol.hpp>

#include <iostream>
#include <cassert>
#include <cmath>

struct foo {
private:
    std::string name;
public:
    foo(std::string name): name(std::string(name)) {}

    void print() {
        std::cout << name << '\n';
    }

    int test(int x) {
        return name.length() + x;
    }
};

struct vector {
private:
    float x = 0;
    float y = 0;
public:
    vector() = default;
    vector(float x): x(x) {}
    vector(float x, float y): x(x), y(y) {}

    bool is_unit() const {
        return (x * x + y * y) == 1.f;
    }
};

struct variables {
    bool low_gravity = false;
    int boost_level = 0;

};

int main() {
	std::cout << "=== usertype example ===" << std::endl;

    sol::state lua;
    lua.open_libraries(sol::lib::base, sol::lib::math);

    // the simplest way to create a class is through
    // sol::state::new_userdata
    // the first template is the class type
    // the rest are the constructor parameters
    // using new_userdata you can only have one constructor


    // you must make sure that the name of the function
    // goes before the member function pointer
    lua.new_usertype<foo, std::string>("foo", "print", &foo::print, "test", &foo::test);

    // making the class from lua is simple
    // same with calling member functions
    lua.script("x = foo.new('test')\n"
               "x:print()\n"
               "y = x:test(10)");

    auto y = lua.get<int>("y");
    std::cout << y << std::endl; // show 14

    // if you want a class to have more than one constructor
    // the way to do so is through set_userdata and creating
    // a userdata yourself with constructor types

    {
        // Notice the brace: this means we're in a new scope
        // first, define the different types of constructors
		// notice here that the return type 
		// on the function-type doesn't exactly matter,
		// which allows you to use a shorter class name/void 
		// if necessary
        sol::constructors<vector(), vector(float), void(float, float)> ctor;

        // the only template parameter is the class type
        // the first argument of construction is the name
        // second is the constructor types
        // then the rest are function name and member function pointer pairs
        sol::usertype<vector> utype(ctor, "is_unit", &vector::is_unit);

        // then you must register it
        lua.set_usertype("vector", utype);
        // You can throw away the usertype after you set it: you do NOT
        // have to keep it around
        // cleanup happens automagically
    }
    // calling it is the same as new_userdata

    lua.script("v = vector.new()\n"
               "v = vector.new(12)\n"
               "v = vector.new(10, 10)\n"
               "assert(not v:is_unit())\n");

    // You can even have C++-like member-variable-access
    // just pass is public member variables in the same style as functions
    lua.new_usertype<variables>("variables", "low_gravity", &variables::low_gravity, "boost_level", &variables::boost_level);

    // making the class from lua is simple
    // same with calling member functions/variables
    lua.script("local vars = variables.new()\n"
               "assert(not vars.low_gravity)\n"
               "vars.low_gravity = true\n"
               "local x = vars.low_gravity\n"
               "assert(x)");

	std::cout << std::endl;

}