From 5a9cc57a5ef75a28cd887715175a5a18db58616e Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Thu, 17 Jul 2014 14:09:50 -0300
Subject: change in GCObject: instead of being a union, it is now a structure
 with the common header of all collectable objects; union is used only for
 conversions. (Goal is to be able to check that the cast 'obj2gco' can have a
 check to ensure that object being converted is really a collectable object.).
 This is the first step in the change.

---
 lobject.h | 16 +++++++++-------
 lstate.h  | 33 +++++++++++++++++++++------------
 2 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/lobject.h b/lobject.h
index 72820220..d55a347f 100644
--- a/lobject.h
+++ b/lobject.h
@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.h,v 2.93 2014/05/29 19:30:07 roberto Exp roberto $
+** $Id: lobject.h,v 2.94 2014/06/19 18:39:36 roberto Exp roberto $
 ** Type definitions for Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -69,9 +69,9 @@
 
 
 /*
-** Union of all collectable objects
+** Common type for all collectable objects
 */
-typedef union GCObject GCObject;
+typedef struct GCObject GCObject;
 
 
 /*
@@ -82,11 +82,13 @@ typedef union GCObject GCObject;
 
 
 /*
-** Common header in struct form
+** Common type has only the common header
 */
-typedef struct GCheader {
-  CommonHeader;
-} GCheader;
+struct GCObject {
+  struct {
+    CommonHeader;
+  } gch;
+};
 
 
 
diff --git a/lstate.h b/lstate.h
index 8b7031f8..e7feb099 100644
--- a/lstate.h
+++ b/lstate.h
@@ -1,5 +1,5 @@
 /*
-** $Id: lstate.h,v 2.107 2014/06/12 19:07:30 roberto Exp roberto $
+** $Id: lstate.h,v 2.108 2014/07/17 13:53:37 roberto Exp roberto $
 ** Global State
 ** See Copyright Notice in lua.h
 */
@@ -172,8 +172,8 @@ struct lua_State {
 /*
 ** Union of all collectable objects
 */
-union GCObject {
-  GCheader gch;  /* common header */
+union GCUnion {
+  GCObject gc;  /* common header */
   union TString ts;
   union Udata u;
   union Closure cl;
@@ -185,22 +185,31 @@ union GCObject {
 
 #define gch(o)		(&(o)->gch)
 
+#define cast_u(o)	cast(union GCUnion *, (o))
+
 /* macros to convert a GCObject into a specific value */
 #define rawgco2ts(o)  \
-	check_exp(novariant((o)->gch.tt) == LUA_TSTRING, &((o)->ts))
+	check_exp(novariant((o)->gch.tt) == LUA_TSTRING, &((cast_u(o))->ts))
 #define gco2ts(o)	(&rawgco2ts(o)->tsv)
-#define rawgco2u(o)	check_exp((o)->gch.tt == LUA_TUSERDATA, &((o)->u))
+#define rawgco2u(o)  \
+	check_exp((o)->gch.tt == LUA_TUSERDATA, &((cast_u(o))->u))
 #define gco2u(o)	(&rawgco2u(o)->uv)
-#define gco2lcl(o)	check_exp((o)->gch.tt == LUA_TLCL, &((o)->cl.l))
-#define gco2ccl(o)	check_exp((o)->gch.tt == LUA_TCCL, &((o)->cl.c))
+#define gco2lcl(o)  \
+	check_exp((o)->gch.tt == LUA_TLCL, &((cast_u(o))->cl.l))
+#define gco2ccl(o)  \
+	check_exp((o)->gch.tt == LUA_TCCL, &((cast_u(o))->cl.c))
 #define gco2cl(o)  \
-	check_exp(novariant((o)->gch.tt) == LUA_TFUNCTION, &((o)->cl))
-#define gco2t(o)	check_exp((o)->gch.tt == LUA_TTABLE, &((o)->h))
-#define gco2p(o)	check_exp((o)->gch.tt == LUA_TPROTO, &((o)->p))
-#define gco2th(o)	check_exp((o)->gch.tt == LUA_TTHREAD, &((o)->th))
+	check_exp(novariant((o)->gch.tt) == LUA_TFUNCTION, &((cast_u(o))->cl))
+#define gco2t(o)  \
+	check_exp((o)->gch.tt == LUA_TTABLE, &((cast_u(o))->h))
+#define gco2p(o)  \
+	check_exp((o)->gch.tt == LUA_TPROTO, &((cast_u(o))->p))
+#define gco2th(o)  \
+	check_exp((o)->gch.tt == LUA_TTHREAD, &((cast_u(o))->th))
+
 
 /* macro to convert any Lua object into a GCObject */
-#define obj2gco(v)	(cast(GCObject *, (v)))
+#define obj2gco(v)	(&(cast_u(v)->gc))
 
 
 /* actual number of total bytes allocated */
-- 
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