sol2/examples/userdata.cpp

#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;
    }
};

int main() {
    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_userdata<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");
    assert(y == 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

    // first, define the different types of constructors
    sol::constructors<sol::types<>, sol::types<float>, sol::types<float, float>> ctor;

    // second, create a new userdata class
    // note that you have to make sure the class is
    // alive throughout the scope of the program.

    // 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::userdata<vector> udata("vector", ctor, "is_unit", &vector::is_unit);

    // then you must register it
    lua.set_userdata(udata);

    // 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");
}