3 files changed, 104 insertions, 57 deletions

diff --git a/examples/oop_example.c b/examples/oop_example.c
index 89f5994..859bd03 100644
--- a/examples/oop_example.c
+++ b/examples/oop_example.c
@@ -3,16 +3,18 @@
 #include <stdlib.h>
 #include "../common.h"
 
+#define SQR(x) ((x) * (x))
+
 const char *point_tname = "nerv.Point";
+const char *better_point_tname = "nerv.BetterPoint";
 
 typedef struct {
     double x, y;
-    int arr[100];
 } Point;
 
-static int point_get_sinx (lua_State *L) {
+static int point_norm (lua_State *L) {
     Point *p = luaT_checkudata(L, 1, point_tname);
-    lua_pushnumber(L, sin(p->x));
+    lua_pushnumber(L, sqrt(SQR(p->x) + SQR(p->y)));
     return 1;
 }
 
@@ -22,67 +24,104 @@ static int point_set_x (lua_State *L) {
     return 0;
 }
 
-
-static int point_get_y(lua_State *L) {
+static int point_set_y (lua_State *L) {
     Point *p = luaT_checkudata(L, 1, point_tname);
-    lua_pushnumber(L, sin(p->x));
-    return 1;
+    p->y = luaL_checknumber(L, 2);
+    return 0;
 }
 
-static int point_newindex(lua_State *L) {
-    Point *p = luaT_checkudata(L, 1, point_tname);
-    if (lua_isnumber(L, 2))
-    {
-        int d = luaL_checkinteger(L, 2);
-        double v = luaL_checknumber(L, 3);
-        if (0 <= d && d < 100)
-            p->arr[d] = v;
-        lua_pushboolean(L, 1);
-        return 1;
-    }
-    else
-    {
-        lua_pushboolean(L, 0);
-        return 1;
-    }
+/* generic constructor */
+void point_new_(Point *self, double x, double y) {
+    self->x = x;
+    self->y = y;
 }
 
-static int point_index(lua_State *L) {
-    Point *p = luaT_checkudata(L, 1, point_tname);
-    if (lua_isnumber(L, 2))
-    {
-        int d = luaL_checkinteger(L, 2);
-        if (0 <= d && d < 100)
-            lua_pushnumber(L, p->arr[d]);
-        lua_pushboolean(L, 1);
-        return 2;
-    }
-    else
-    {
-        lua_pushboolean(L, 0);
-        return 1;
-    }
+int point_new(lua_State *L) {
+    /* `_new` function should create the object itself */
+    Point *self = (Point *)malloc(sizeof(Point));
+    point_new_(self, luaL_checknumber(L, 1), luaL_checknumber(L, 2));
+    luaT_pushudata(L, self, point_tname);
+    fprintf(stderr, "[example] %s constructor is invoked\n",
+            point_tname);
+    return 1;
 }
 
-int point_new(lua_State *L) {
+int point___init(lua_State *L) {
+    /* The difference between this function and `_new` function is that this
+     * one is called by subclass of Point implemented in Lua, although it
+     * basically does the same thing as `_new`. Also, it can read the empty
+     * object (table) from the stack. (In this example, the table is ignored.) */
     Point *self = (Point *)malloc(sizeof(Point));
-    self->x = 0;
-    self->y = 0;
+    point_new_(self, luaL_checknumber(L, 2), luaL_checknumber(L, 3));
     luaT_pushudata(L, self, point_tname);
+    fprintf(stderr, "[example] A subclass has invoked `__init`\n");
     return 1;
 }
 
-static const luaL_Reg point[] = {
-    {"get_sinx", point_get_sinx},
+static const luaL_Reg point_methods[] = {
     {"set_x", point_set_x},
-    {"get_y", point_get_y},
-    {"__index__", point_index},
-    {"__newindex__", point_newindex},
+    {"set_y", point_set_y},
+    {"__init", point___init},
+    {"norm", point_norm},
+    {NULL, NULL}
+};
+
+
+/* the subclass method overrides the one from baseclass */
+static int better_point_norm (lua_State *L) {
+    Point *p = luaT_checkudata(L, 1, point_tname);
+    lua_pushnumber(L, fabs(p->x) + fabs(p->y));
+    return 1;
+}
+
+int better_point_new(lua_State *L) {
+    /* `_new` function should create the object itself */
+    Point *self = (Point *)malloc(sizeof(Point));
+    point_new_(self, luaL_checknumber(L, 1), luaL_checknumber(L, 2));
+    luaT_pushudata(L, self, better_point_tname);
+    fprintf(stderr, "[example] %s constructor is invoked\n",
+            better_point_tname);
+    return 1;
+}
+
+int better_point___init(lua_State *L) {
+    /* The difference between this function and `_new` function is that this
+     * one is called by subclass of Point implemented in Lua, although it
+     * basically does the same thing as `_new`. Also, it can read the empty
+     * object (table) from the stack. (In this example, the table is ignored.) */
+    Point *self = (Point *)malloc(sizeof(Point));
+    point_new_(self, luaL_checknumber(L, 2), luaL_checknumber(L, 3));
+    luaT_pushudata(L, self, better_point_tname);
+    fprintf(stderr, "[example] A subclass has invoked `__init`\n");
+    return 1;
+}
+
+static const luaL_Reg better_point_methods[] = {
+    {"norm", better_point_norm},
+    {"__init", better_point___init},
     {NULL, NULL}
 };
 
 void nerv_point_init(lua_State *L) {
-    luaT_newmetatable(L, "nerv.Point", NULL, point_new, NULL, NULL);
-    luaL_register(L, NULL, point);
+    /* create a class and let luaT know */
+    luaT_newmetatable(L, point_tname, NULL, point_new, NULL, NULL);
+    /* register member functions */
+    luaL_register(L, NULL, point_methods);
+    /* keep the stack balanced, see `nerv.c` */
+    lua_pop(L, 1);
+}
+
+void nerv_better_point_init(lua_State *L) {
+    /* create a class and let luaT know */
+    luaT_newmetatable(L, better_point_tname, point_tname,
+                        better_point_new, NULL, NULL);
+    /* register member functions */
+    luaL_register(L, NULL, better_point_methods);
+    /* keep the stack balanced, see `nerv.c` */
     lua_pop(L, 1);
 }
+
+void nerv_example_init(lua_State *L) {
+    nerv_point_init(L);
+    nerv_better_point_init(L);
+}
diff --git a/examples/oop_example.lua b/examples/oop_example.lua
index 45da36e..712387b 100644
--- a/examples/oop_example.lua
+++ b/examples/oop_example.lua
@@ -1,7 +1,15 @@
-a = nerv.Point()
-print(a:get_sinx())
-a:set_x(3.14)
-print(a:get_sinx())
-print(a[2])
-a[2] = 3
-print(a[2])
+p = nerv.Point(0, 0) -- create a Point instance
+print(p)
+print(p:norm()) -- get 2-norm of the Point
+p:set_x(1.0)
+p:set_y(2.0)
+print(p:norm()) -- get 2-norm of the Point
+
+p = nerv.BetterPoint(1, 2)
+print(p)
+print(p:norm()) --get 1-norm of the Point
+
+-- create a subclass using lua
+local EvenBetterPoint = nerv.class('nerv.EvenBetterPoint', 'nerv.BetterPoint')
+bp = nerv.EvenBetterPoint(1, 2)
+print(p:norm())
diff --git a/nerv.c b/nerv.c
index 0bc661e..5693d68 100644
--- a/nerv.c
+++ b/nerv.c
@@ -1,6 +1,6 @@
 #include "common.h"
 
-extern void nerv_point_init(lua_State *L);
+extern void nerv_example_init(lua_State *L);
 extern void nerv_matrix_init(lua_State *L);
 extern void nerv_param_init(lua_State *L);
 
@@ -30,7 +30,7 @@ int luaopen_libnerv(lua_State *L) {
      * Also note that they can make use of the value at top of the stack which
      * references to the `nerv` global table. */
     nerv_utils_init(L);
-    nerv_point_init(L);
+    nerv_example_init(L);
     nerv_matrix_init(L);
     nerv_param_init(L);
     return 1;