clear docs on exists wrt autovivification

[p5sagit/p5-mst-13.2.git] / mro.c

diff --git a/mro.c b/mro.c
index 13dd70a..ffb72ab 100644 (file)
--- a/mro.c
+++ b/mro.c
@@ -185,9 +185,32 @@ S_mro_get_linear_isa_dfs(pTHX_ HV *stash, I32 level)
            }
            while(subrv_items--) {
                SV *const subsv = *subrv_p++;
-               if(!hv_exists_ent(stored, subsv, 0)) {
-                   (void)hv_store_ent(stored, subsv, &PL_sv_undef, 0);
-                   av_push(retval, newSVsv(subsv));
+               /* LVALUE fetch will create a new undefined SV if necessary
+                */
+               HE *const he = hv_fetch_ent(stored, subsv, 1, 0);
+               assert(he);
+               if(HeVAL(he) != &PL_sv_undef) {
+                   /* It was newly created.  Steal it for our new SV, and
+                      replace it in the hash with the "real" thing.  */
+                   SV *const val = HeVAL(he);
+                   HEK *const key = HeKEY_hek(he);
+
+                   HeVAL(he) = &PL_sv_undef;
+                   /* Save copying by making a shared hash key scalar. We
+                      inline this here rather than calling Perl_newSVpvn_share
+                      because we already have the scalar, and we already have
+                      the hash key.  */
+                   assert(SvTYPE(val) == SVt_NULL);
+                   sv_upgrade(val, SVt_PV);
+                   SvPV_set(val, HEK_KEY(share_hek_hek(key)));
+                   SvCUR_set(val, HEK_LEN(key));
+                   SvREADONLY_on(val);
+                   SvFAKE_on(val);
+                   SvPOK_on(val);
+                   if (HEK_UTF8(key))
+                       SvUTF8_on(val);
+
+                   av_push(retval, val);
                }
             }
         }