Add examples for userdata

examples/userdata.cpp

@@ -0,0 +1,85 @@
+#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");
+}