Re^5: Tim O'Reilly on Perl

[holli]

Will we have lvalue methods in Perl 6? Because that's what really bugs me, about Perl 5 OO.

$obj->SetProperty("something");

is just ugly, compared to the shiny elegance of

$obj->Property = "something";

[blazar]

You bet you will have them! Only such a method will be spelled 'is rw'. Well, until Larry changes his mind on this...

[eric256]

It does indeed have that already.

use v6;
class test {
  has $.Property;
}
my $testing = new test;
$testing.Property = 5;
$testing.Property.say;

I beleive that it actualy uses a Proxy object with lvalue attributes, but don't quote me on that. ;)

[chromatic]

Gah, ambiguous indirect object notation went away in Perl 6. Mark the invocant explicitly:

my $testing = new test:;

Or make a method call look like a method call:

my $testing = test.new()

[eric256]

Since the objects have no obvious public method new it makes more sense (to me) to call them in a magical sort of way. I don't see what adding the : to the end of the name does for anything. It certainly doesn't make it clearer. However new Object is pretty standard across many languages while your two examples are not. I would agree with using your second form on everything except new. It reads easier when you say $x is a (=) new Object.

[tlm]

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

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.)

[holli]

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;
}

[Zaxo]

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.