Add &CORE::undef

In the error message, we can’t say ‘&CORE::undef operator’, so we
should be using the op name, rather than the op description.

Instead of using OP_NAME(PL_op->op_next), which would expand to

    PL_op->op_next->op_type == OP_CUSTOM
	? XopENTRY(Perl_custom_op_xop(aTHX_ PL_op->op_next), xop_name)
	: PL_op_name[PL_op->op_next->op_type]

we can simply use PL_op_name[opnum], which should be quicker.

pp_undef can already handle nulls on the stack.

There is one remaining problem.  If &CORE::undef(\*_) is called, *_
will be undefined while @_ is localised during the sub call, so it
won’t have the same effect as undef *_.  I don’t know whether this
should be considered a bug or not, but I could solve it by making
pp_undef an XSUB.

1 files changed, 1 insertions, 1 deletions

diff --git a/gv.c b/gv.c
index acf7f9bf02..ab2aef1228 100644
--- a/gv.c
+++ b/gv.c
@@ -471,7 +471,7 @@ S_maybe_add_coresub(pTHX_ HV * const stash, GV *gv,
     case KEY_qx   : case KEY_redo : case KEY_require: case KEY_return:
     case KEY_s    : case KEY_say  : case KEY_sort   :
     case KEY_state: case KEY_sub  :
-    case KEY_tr   : case KEY_undef: case KEY_UNITCHECK: case KEY_unless:
+    case KEY_tr   : case KEY_UNITCHECK: case KEY_unless:
     case KEY_until: case KEY_use  : case KEY_when     : case KEY_while :
     case KEY_x    : case KEY_xor  : case KEY_y        :
 	return NULL;