Use MRB_TT_EXCEPTION in exception object.

src/error.c

@@ -15,6 +15,7 @@
 #include "mruby/variable.h"
 #include "mruby/debug.h"
 #include "mruby/error.h"
+#include "mruby/class.h"
 #include "mrb_throw.h"
 
 mrb_value
@@ -442,6 +443,7 @@ mrb_init_exception(mrb_state *mrb)
   struct RClass *exception, *runtime_error, *script_error;
 
   mrb->eException_class = exception = mrb_define_class(mrb, "Exception", mrb->object_class); /* 15.2.22 */
+  MRB_SET_INSTANCE_TT(exception, MRB_TT_EXCEPTION);
   mrb_define_class_method(mrb, exception, "exception", mrb_instance_new,  MRB_ARGS_ANY());
   mrb_define_method(mrb, exception, "exception",       exc_exception,     MRB_ARGS_ANY());
   mrb_define_method(mrb, exception, "initialize",      exc_initialize,    MRB_ARGS_ANY());

src/gc.c

@@ -16,6 +16,7 @@
 #include "mruby/string.h"
 #include "mruby/variable.h"
 #include "mruby/gc.h"
+#include "mruby/error.h"
 
 /*
   = Tri-color Incremental Garbage Collection
@@ -107,6 +108,7 @@ typedef struct {
     struct RRange range;
     struct RData data;
     struct RProc proc;
+    struct RException exc;
 #ifdef MRB_WORD_BOXING
     struct RFloat floatv;
     struct RCptr cptr;
@@ -513,6 +515,7 @@ gc_mark_children(mrb_state *mrb, struct RBasic *obj)
 
   case MRB_TT_OBJECT:
   case MRB_TT_DATA:
+  case MRB_TT_EXCEPTION:
     mrb_gc_mark_iv(mrb, (struct RObject*)obj);
     break;
 
@@ -612,6 +615,7 @@ obj_free(mrb_state *mrb, struct RBasic *obj)
 #endif
 
   case MRB_TT_OBJECT:
+  case MRB_TT_EXCEPTION:
     mrb_gc_free_iv(mrb, (struct RObject*)obj);
     break;
 
@@ -747,6 +751,7 @@ gc_gray_mark(mrb_state *mrb, struct RBasic *obj)
 
   case MRB_TT_OBJECT:
   case MRB_TT_DATA:
+  case MRB_TT_EXCEPTION:
     children += mrb_gc_mark_iv_size(mrb, (struct RObject*)obj);
     break;
 

src/kernel.c

@@ -275,6 +275,7 @@ init_copy(mrb_state *mrb, mrb_value dest, mrb_value obj)
     case MRB_TT_SCLASS:
     case MRB_TT_HASH:
     case MRB_TT_DATA:
+    case MRB_TT_EXCEPTION:
       mrb_iv_copy(mrb, dest, obj);
       break;
 

src/variable.c

@@ -459,6 +459,7 @@ obj_iv_p(mrb_value obj)
     case MRB_TT_SCLASS:
     case MRB_TT_HASH:
     case MRB_TT_DATA:
+    case MRB_TT_EXCEPTION:
       return TRUE;
     default:
       return FALSE;