Lua C APIを触ってみた.

l_geom.c

#include <lua5.2/lua.h>
#include <lua5.2/lualib.h>
#include <lua5.2/lauxlib.h>

#define POINT2D_CLASS "Point2D"
typedef struct point2d { int x; int y; } point2d;

static void create_point2d(lua_State *L, int x, int y) {
    point2d* pnt = (point2d *)lua_newuserdata(L, sizeof(point2d));
    luaL_getmetatable(L, POINT2D_CLASS);
    lua_setmetatable(L, -2);
    pnt->x = x;
    pnt->y = y;
}

static int point2d_constructor(lua_State *L) {
    int x = luaL_checkinteger(L, 1);
    int y = luaL_checkinteger(L, 2);
    create_point2d(L, x, y);
    return 1;
}

static int point2d_add(lua_State *L) {
    point2d* lhs = luaL_checkudata(L, 1, POINT2D_CLASS);
    point2d* rhs = luaL_checkudata(L, 2, POINT2D_CLASS);
    create_point2d(L, lhs->x + rhs->x, lhs->y + rhs->y);
    return 1;
}

static int point2d_sub(lua_State *L) {
    point2d* lhs = luaL_checkudata(L, 1, POINT2D_CLASS);
    point2d* rhs = luaL_checkudata(L, 2, POINT2D_CLASS);
    create_point2d(L, lhs->x - rhs->x, lhs->y - rhs->y);
    return 1;
}

static int point2d_setx(lua_State *L) {
    point2d* pnt = luaL_checkudata(L, 1, POINT2D_CLASS);
    int x = luaL_checkinteger(L, 2);
    pnt->x = x;
    return 0;
}

static int point2d_sety(lua_State *L) {
    point2d* pnt = luaL_checkudata(L, 1, POINT2D_CLASS);
    int y = luaL_checkinteger(L, 2);
    pnt->y = y;
    return 0;
}

static int point2d_getx(lua_State *L) {
    point2d* pnt = luaL_checkudata(L, 1, POINT2D_CLASS);
    lua_pushinteger(L, pnt->x);
    return 1;
}

static int point2d_gety(lua_State *L) {
    point2d* pnt = luaL_checkudata(L, 1, POINT2D_CLASS);
    lua_pushinteger(L, pnt->y);
    return 1;
}

static int point2d_tostring(lua_State *L) {
    point2d* pnt = luaL_checkudata(L, 1, POINT2D_CLASS);
    lua_pushfstring(L, "Point2D(%d, %d)", pnt->x, pnt->y);
    return 1;
}

static void register_point2d_methods(lua_State *L) {
    static const luaL_Reg point2d_methods[] = {
        { "Add",        point2d_add      },
        { "Sub",        point2d_sub      },
        { "SetX",       point2d_setx     },
        { "SetY",       point2d_sety     },
        { "GetX",       point2d_getx     },
        { "GetY",       point2d_gety     },
        { "__add",      point2d_add      },
        { "__sub",      point2d_sub      },
        { "__tostring", point2d_tostring },
        { NULL, NULL }
    };

    luaL_newmetatable(L, POINT2D_CLASS);
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");
    luaL_setfuncs(L, point2d_methods, 0);
    lua_pop(L, 1);
}

LUALIB_API int luaopen_geom(lua_State *L) {
    static const luaL_Reg geom_lib[] = {
        { "Point2D", point2d_constructor },
        { NULL, NULL }
    };
    register_point2d_methods(L);
    luaL_newlib(L, geom_lib);
    return 1;
}