Reimplement $[ as a module

This commit reimplements $[ using PL_check hooks, custom pp func-
tions and ties.

Outside of its compile-time use, $[ is now parsed as a simple varia-
ble, so function calls like foo($[) are permitted, which was not the
case with the former implementation removed by e1dccc0.  I consider
that a bug fix.

The ‘That use of $[ is unsupported’ errors are out of necessity
deferred to run-time and implemented by a tied $[.

Indices between 0 and the array base are now treated consistently, as
are indices between a negative array base and zero.  That, too, is
a bug fix.

1 files changed, 0 insertions, 4 deletions

diff --git a/mg.c b/mg.c
index 1b24ce85d6..8c986a5fd7 100644
--- a/mg.c
+++ b/mg.c
@@ -2723,10 +2723,6 @@ Perl_magic_set(pTHX_ SV *sv, MAGIC *mg)
 	    PL_ors_sv = NULL;
 	}
 	break;
-    case '[':
-	if (SvIV(sv) != 0)
-	    Perl_croak(aTHX_ "Assigning non-zero to $[ is no longer possible");
-	break;
     case '?':
 #ifdef COMPLEX_STATUS
 	if (PL_localizing == 2) {