Not quite right Rob :)
Rob Hanson wrote:
>
> > But I'm wondering if there is another way
> > (like the Java "private variable") to say
> > "all class variables declared here are unique
> > to each instance"?
>
> It sounds like you are trying to link how OO-Perl works with OO-Java... and
> that is only going to make your head spin. What you really need to do is
> understand what bless really does, and that OO-Perl isn't really OO in the
> usual sense (but it works like it is).
>
> In Perl an "object" is really just a scalar variable that has been blessed.
> Blessing adds an attribute to the scalar variable which is supposed to
> represent the "type" of scalar. The only requirement is that the bless
> scalar must be a reference.
>
> my $x = "foo";
> my $y = bless \$x, "bar";
> print $y;
> # PRINTS: bar=SCALAR(0xa01ed1c)
>
> Here $y is a reference to a scalar (hence the "SCALAR(0xa01ed1c)"), and it
> has been tagged as type "bar".
>
> That is all bless does.
>
> Now the next part is the magic that Perl does...
>
> $x->do_stuff;
>
> Here $x does what looks like a method call. Perl will look at the "type" of
> $x, which is "foo", then try to execute do_stuff() in the "foo" package.
The type of $x is 'bar' - you just said so above. Its value is
'foo', but usually you will want a lot more than just a single
scalar value in your object, so they are more usually hashes
as you say below.
> The first argument of this call will always be $x, like this:
>
> foo:do_stuff($x);
THis should be
bar::do_stuff($x)
> This call does exactly the same thing as above.
>
> Now when you talk about instance variables, realize that there is no true
> object instance in Perl. It is just a reference tagged with a "type"... the
> rest is all smoke and mirrors.
>
> So to emmulate instance variables you can use a hash reference instead of a
> scalar reference, like this:
>
> my %x = (field1 => 'val1', field2 => 'val2');
> my $y = bless \%x, "bar";
>
> Now $y is just a hash reference, so this stuff still works:
>
> print $y->{field1};
> print $y->{field2};
>
> ...And $y is also blessed, meaning you can emulate calling methods like I
> did earlier.
>
> Now you can still emulate private variables, but again, it's more smoke and
> mirrors. Without getting into the details (look at 'tie' for more info) you
> can just use the Tie::SecureHash module. It emulated public, protected, and
> private variables.
>
> http://search.cpan.org/author/DCONWAY/Tie-SecureHash-1.03/SecureHash.pm
It would be a Good Idea to get simple objects working before considering
private variables.
Cheers,
Rob
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