Add single-term prototype

The C<+> prototype is a special alternative to C<$> that will act like
C<\[@%]> when given a literal array or hash variable, but will otherwise
force scalar context on the argument.  This is useful for functions which
should accept either a literal array or an array reference as the argument:

    sub smartpush (+@) {
        my $aref = shift;
        die "Not an array or arrayref" unless ref $aref eq 'ARRAY';
        push @$aref, @_;
    }

When using the C<+> prototype, your function must check that the argument
is of an acceptable type.

1 files changed, 12 insertions, 0 deletions

diff --git a/op.c b/op.c
index ac9a41e9d2..469d48d0bd 100644
--- a/op.c
+++ b/op.c
@@ -8735,6 +8735,18 @@ Perl_ck_entersub_args_proto(pTHX_ OP *entersubop, GV *namegv, SV *protosv)
 		}
 		scalar(aop);
 		break;
+	    case '+':
+		proto++;
+		arg++;
+		if (o3->op_type == OP_RV2AV ||
+		    o3->op_type == OP_PADAV ||
+		    o3->op_type == OP_RV2HV ||
+		    o3->op_type == OP_PADHV
+		) {
+		    goto wrapref;
+		}
+		scalar(aop);
+		break;
 	    case '[': case ']':
 		goto oops;
 		break;