What is wrong with my SWIG typemap?

Question

I created a SWIG typemap for my function.

%typemap(in) (int width, int height, lua_State *L)
{
    if (!lua_isnumber(L, -1) || !lua_isnumber(L, -2))
        SWIG_exception(SWIG_RuntimeError, "argument mismatch: number expected");
    $1 = lua_tonumber(L, -1);
    $2 = lua_tonumber(L, -2);
    $3 = L;
}

But it doesn't work if I try to call the function in Lua.

I call this function like the following in Lua.

createWindow(500,300)

I just want to pass width, height from Lua to this function.

How can I fix the typemap to make it work?

Answer 1

Multi-argument typemaps won't do the trick here because they are designed to map a single Lua argument to multiple C++ arguments. You can help yourself with a default argument here. This is done using %typemap(default). We tell SWIG to default any lua_State *L argument to the instance used by SWIG.

%module window

%{
#include <iostream>

void createWindow(int width, int height, lua_State *L) {
    std::cout << "Creating window of size " << width << "x" << height << '\n'
              << "Number of arguments: " << lua_gettop(L) << '\n';
}
%}

%typemap(default) (lua_State *L) {
    $1 = L;
}

void createWindow(int width, int height, lua_State *L);

local window = require("window")
window.createWindow(500,300)

$ lua5.2 test.lua
Creating window of size 500x300
Number of arguments: 2