On Mon, Jun 25, 2001 at 12:47:41PM -0700, David Whipp wrote:
>> What's wrong with multiple inheritance?
> You have to create a whole load of extra classes whose only
> purpose is to define a list of superclasses. Compare:
This sounds a lot like the case I had with a
<buzzword type="cheesy">content-syndication</buzzword> system I'm
working on.
Basically, I wanted to create a Feed-object that inherits from any
Fetch-class and any Parse-class. Something like this:
bless $obj1, qw/Fetch::LWP Parse::HTML/;
bless $obj2, qw/Fetch::POP3 Parse::CSV/;
but then I realized that since the Fetch and Parse-classes never diddled
with $self, I didn't need inheritance at all. Delegation was more than
good enough in my case.
I ended up with something like this (simplified a bit):
package Feed;
sub new {
my $class = shift;
my %args = @_;
my $f = $args{FETCH}->new;
my $p = $args{PARSE}->new;
bless {FETCH => $f, PARSE => $p} => $class;
}
sub fetch {
my $self = shift;
return $self->{FETCH}->fetch(@_);
}
sub parse {
my $self = shift;
return $self->{PARSE}->parse(@_);
}
sub cleanup {
my $self = shift;
$self->{FETCH}->cleanup(@_);
$self->{PARSE}->cleanup(@_);
}
etc..
which works very well.
The downside is of course that I need to make a small stub for every
single function I want to delegate. Since it's only a few function I
need from the classes, it's not a big problem. If you have 50 functions
in each class, it could be a hassle.
I haven't given it much thought, but I imagine the cleanup-method could
be difficoult to implement with inheritance.
I don't know if delegation is the solution in your case though. And I
certainly can't claim that it is the solution in every "multibless"
case. But it worked for me :)
--
Trond Michelsen
