#!/usr/bin/perl
use strict;
use warnings;

use Hook::LexWrap;

{
    my $foo;
    sub foo { @_ ? $foo = shift : $foo; }

    my $wrapper = wrap *foo,
        pre => sub {
            warn 0+@_, " @_";
            # splice @_, 0, 1, lc( $_[0]) if @_ > 1; # bad
            $_[0] = lc $_[0] if @_ > 1;  #new
            warn 0+@_, " @_";
        },
        post => sub {
            $_[-1] = 
                wantarray ?
                [ map {uc} @{$_[-1]} ] :
                uc $_[-1]
        };
    sub wrapper () :lvalue { $wrapper } # keeps the cloistered
                                        # lexwrap alive

    sub _foo () :lvalue { $foo } # inspection hatch
}

my $str = 'Quux';
my $tmp = $str;
printf "Given $str, wrapped setter reports %s, backdoor shows %s, arg is now %s.\n",
    foo($tmp), _foo, $tmp;    # setter
printf "Wrapped getter reports %s, and backdoor shows %s\n",
    foo(), _foo; # getter

__END__
2 Quux ARRAY(0x804b3f8) at hlw.pl line 13.
2 quux ARRAY(0x804b3f8) at hlw.pl line 15.
Given Quux, wrapped setter reports QUUX, backdoor shows Quux, arg is now Quux.
1 ARRAY(0x804b50c) at hlw.pl line 13.
1 ARRAY(0x804b50c) at hlw.pl line 15.
Wrapped getter reports QUUX, and backdoor shows Quux