Make state $zok = slosh(); behave as the Perl 6 design with an implicit

START block. First time through, call slosh() and assign to $zok.
Subsequently neither call slosh() nor assign to $zok. Adds a new op
ONCE to control the conditonal call and assign. No change to list
context, so state ($zok) = slosh() and (state $zok) = ... etc will
still repeatedly evaluate and assign. [Can't fix that before 5.10]
Use as an RVALUE is as Larry's design - my $boff = state $zok = ...;
will evaluate, assign and return first time, and subsequently act as if
it were written my $boff = $zok;
FIXME - state $zok = ...; won't deparse - I believe op->op_last isn't
being correctly set on the sassign, but I don't know how to fix this.
This change may be backed out before 5.10.

p4raw-id: //depot/perl@31798

1 files changed, 13 insertions, 0 deletions

diff --git a/pp.c b/pp.c
index dbfc95c567..bc84f6086d 100644
--- a/pp.c
+++ b/pp.c
@@ -4932,6 +4932,19 @@ PP(pp_split)
     RETURN;
 }
 
+PP(pp_once)
+{
+    dSP;
+    SV *const sv = PAD_SVl(PL_op->op_targ);
+
+    if (SvPADSTALE(sv)) {
+	/* First time. */
+	SvPADSTALE_off(sv);
+	RETURNOP(cLOGOP->op_other);
+    }
+    RETURNOP(cLOGOP->op_next);
+}
+
 PP(pp_lock)
 {
     dVAR;