Details

Several small improvements (code style, warnings, comments, more tests),
in particular:

- 'lua_topointer' extended to handle strings
- raises an error in 'string.format("%10q")' ('%q' with modifiers)
- in the manual for 'string.format', the term "option" replaced by
  "conversion specifier" (the term used by the C standard)

lapi.c

@@ -414,8 +414,7 @@ LUA_API lua_CFunction lua_tocfunction (lua_State *L, int idx) {
 }
 
 
-LUA_API void *lua_touserdata (lua_State *L, int idx) {
-  const TValue *o = index2value(L, idx);
+static void *touserdata (const TValue *o) {
   switch (ttype(o)) {
     case LUA_TUSERDATA: return getudatamem(uvalue(o));
     case LUA_TLIGHTUSERDATA: return pvalue(o);
@@ -424,23 +423,37 @@ LUA_API void *lua_touserdata (lua_State *L, int idx) {
 }
 
 
+LUA_API void *lua_touserdata (lua_State *L, int idx) {
+  const TValue *o = index2value(L, idx);
+  return touserdata(o);
+}
+
+
 LUA_API lua_State *lua_tothread (lua_State *L, int idx) {
   const TValue *o = index2value(L, idx);
   return (!ttisthread(o)) ? NULL : thvalue(o);
 }
 
 
+/*
+** Returns a pointer to the internal representation of an object.
+** Note that ANSI C does not allow the conversion of a pointer to
+** function to a 'void*', so the conversion here goes through
+** a 'size_t'. (As the returned pointer is only informative, this
+** conversion should not be a problem.)
+*/
 LUA_API const void *lua_topointer (lua_State *L, int idx) {
   const TValue *o = index2value(L, idx);
   switch (ttypetag(o)) {
-    case LUA_TTABLE: return hvalue(o);
-    case LUA_TLCL: return clLvalue(o);
-    case LUA_TCCL: return clCvalue(o);
     case LUA_TLCF: return cast_voidp(cast_sizet(fvalue(o)));
-    case LUA_TTHREAD: return thvalue(o);
-    case LUA_TUSERDATA: return getudatamem(uvalue(o));
-    case LUA_TLIGHTUSERDATA: return pvalue(o);
-    default: return NULL;
+    case LUA_TUSERDATA: case LUA_TLIGHTUSERDATA:
+      return touserdata(o);
+    default: {
+      if (iscollectable(o))
+        return gcvalue(o);
+      else
+        return NULL;
+    }
   }
 }