in reply to Re^5: Tim O'Reilly on Perl
in thread Tim O'Reilly on Perl

Is there something wrong with Perl 5's lvalue attribute? As far as I can tell, it produces rather functional lvalue accessors: 

package Foo;
sub foo : lvalue {
  my $self = shift;
  warn "Only first argument to method foo is used" if @_ > 1;
  $self->{ foo } = shift if @_;
  $self->{ foo };
}

my $x = bless +{}, 'Foo';
$x->foo = 3;
print $x->foo, "\n";
$x->foo++;
print $x->foo, "\n";
$x->foo += 6;
print $x->foo, "\n";

__END__
3
4
10

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I know that user-defined functions with the lvalue attribute, in general, will give wrong results in the debugger, but that's only a problem for those weenies who use the debugger ;-) (Plus, there are good ways around this.)

the lowliest monk

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Re^7: Tim O'Reilly on Perl
by holli (Abbot) on Jul 17, 2005 at 22:41 UTC
    Yeah. The problem with them is one can't check the value before it is set. I would like to have something like 
    sub foo : get
{
  my $self = shift;
  return $self->{_foo};
}

sub foo : set
{
  my $self  = shift;
  my $value = shift;
  
  die "foo is a integer field!\n"
    unless $value =~ /[+-]?[0-9]+/;
  
  $self->{_foo} = $value;
}

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    holli, /regexed monk/
[reply]
[d/l]
      The problem with them is one can't check the value before it is set.

      Oh, but you can. I addressed that in To Validate Data In Lvalue Subs. The Constrained package from that node turned out to have lots of other uses, too. It's now called Tie::Constrained on CPAN.

      After Compline,
      Zaxo

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