lvalue-array.pl

use strict;
use warnings;

{
  package LvalueArray;
  use base 'Tie::Array';
  sub TIEARRAY {
    my ($class, $sub, $params, $afters) = @_;
    my $self = bless [ $sub, $params, $afters ], $class;
  }

  sub STORE {
    $_[0]->[4][$_[1]] = $_[2];
  }

  sub CLEAR {
    $_[0]->[4] = [];
  }
  sub EXTEND {
    $#{$_[0]->[4]} = $_[1]-1;
  }
  sub FETCHSIZE {
    $_[0]->run;
    scalar @{$_[0]->[3]};
  }
  sub FETCH {
    $_[0]->run;
    $_[0]->[3][$_[1]];
  }

  sub run {
    my ($sub, $params, $afters, $result, $store) = @{$_[0]};
    return if $result;
    if ($store) {
      $_[0]->[3] = [($sub->(@$params)) = @$store];
    }
    else {
      $_[0]->[3] = [($sub->(@$params))];
    }
    for my $after (@$afters) {
      $after->(@$params);
    }
  }

  sub DESTROY {
    $_[0]->run;
  }
}

my @foo;
my $foo;
sub foo :lvalue {
  warn "foo running\n";
  @foo;
}


sub wrap :lvalue {
  tie my @array, 'LvalueArray', \&foo, \@_, [sub { warn "after running\n" }];
  @array;
}

(foo()) = (10, 11);
warn "running with after\n";
(wrap()) = (12,13);
warn "running again\n";
warn wrap();