luwra

Luwra

A header-only C++ library which provides a Lua wrapper with minimal overhead.

Usage

Refer to the wiki pages or the documentation. In order to use the library you must clone this repository and add its lib/ folder to your include path.

Have a question? Simply ask or open an issue.

Examples

In the following examples lua refers to an instance of lua_State*.

Easily push values onto the stack:

// Push an integer
luwra::push(lua, 1338);

// Push a number
luwra::push(lua, 13.37);

// Push a boolean
luwra::push(lua, false);

// Push a string
luwra::push(lua, "Hello World");

Or retrieve them:

// Your function
int my_fun(int a, int b) {
    return a + b;
}

// Prepare stack
luwra::push(lua, 13);
luwra::push(lua, 37);

// Apply your function
int result = luwra::apply(lua, my_fun);

// which is equivalent to
int result = luwra::apply(lua, 1, my_fun);

// and equivalent to
int result = luwra::apply(lua, -2, my_fun);

// All of this is essentially syntactic sugar for
int result = my_fun(luwra::read<int>(lua, 1), luwra::read<int>(lua, 2));

Generate a C function which can be used by Lua:

// Assuming your function looks something like this
int my_function(const char* a, int b) {
    // ...
}

// Convert to lua_CFunction
lua_CFunction cfun = LUWRA_WRAP(my_function);

// Do something with it, for example set it as a Lua global function
luwra::setGlobal(lua, "my_function", cfun);

-- Invoke the registered function
local my_result = my_function("Hello World", 1337)
print(my_result)

Or register your own class:

struct Point {
    double x, y;

    Point(double x, double y):
        x(x), y(y)
    {
        std::cout << "Construct Point(" << x << ", " << y << ")" << std::endl;
    }

    ~Point() {
        std::cout << "Destruct Point(" << x << ", " << y << ")" << std::endl;
    }

    void scale(double f) {
        x *= f;
        y *= f;
    }

    std::string __tostring() {
        return "<Point(" + std::to_string(x) + ", " + std::to_string(y) + ")>";
    }
};

// Register the metatable and constructor
luwra::registerUserType<Point(double, double)>(
    lua,

    // Constructor name
    "Point",

    // Methods need to be declared here
    {
        LUWRA_MEMBER(Point, scale),
        LUWRA_MEMBER(Point, x),
        LUWRA_MEMBER(Point, y)
    },

    // Meta methods may be registered aswell
    {
        LUWRA_MEMBER(Point, __tostring)
    }
);

-- Instantiate 'Point'
local point = Point(13, 37)

-- Invoke 'scale' method
point:scale(1.5)

-- Convert to string via '__tostring' meta method
print(point)

-- Read properties 'x' and 'y'
print(point:x(), point:y())

-- Set property 'x'
point:x(4.2)

Requirements

You need a C++14-compliant compiler and at least Lua 5.1 to get this library to work. I recommend using Lua 5.3 or later, to avoid the messy lua_Integer situation. LuaJIT 2.0 seems to work aswell.

Tests

The attached GNU Makefile allows you to run both examples and tests using make examples and make test respectively. You might need to adjust LUA_* variables, so Luwra finds the Lua headers and library.

Assuming all headers are located in /usr/include/lua5.3 and the shared object name is liblua5.3.so, you need to invoke this:

make LUA_INCDIR=/usr/include/lua5.3 LUA_LIBNAME=lua5.3 test

Assertions relying on lua_Integer will fail, due to integer quirks in Lua. This should only concern you if your application expects Lua integers to work like normal integers, because they don't. Since integers are internally stored as floating-point numbers before Lua 5.3, you might consider treating them as such in your application.