use strict;
use warnings;

use Inline C => <<'__EOI__';

/* Something Perl shouldn't free */
static char s[4] = "\x11\x11\x11\x11";

SV* fetch() {
   SV* sv = newSV_type(SVt_PV);
   SvPV_set(sv, s);
   SvPOK_on(sv);
   SvLEN_set(sv, 0);
   SvCUR_set(sv, 4);
   return newRV_noinc(sv);
}

__EOI__

my $ref = fetch();
print(unpack('H*', $$ref), "\n");

$$ref = pack('N', 0x22222222);                 # Bad: Replaces the
$ref = fetch();                                #      PV instead of
print(unpack('H*', $$ref), "\n");              #      modifying it.

substr($$ref, 0, 4, pack('N', 0x33333333));    # OK
$ref = fetch();
print(unpack('H*', $$ref), "\n");

substr($$ref, 0, 4) = pack('N', 0x44444444);   # OK
$ref = fetch();
print(unpack('H*', $$ref), "\n");

substr($$ref, 0) = pack('N', 0x55555555);      # OK
$ref = fetch();
print(unpack('H*', $$ref), "\n");

vec($$ref, 0, 32) = 0x66666666;                # OK
$ref = fetch();
print(unpack('H*', $$ref), "\n");