On Jul 19, [EMAIL PROTECTED] said:
>Whats the difference between class methods and instance methods on perl ?
Syntactically, nothing. In fact, if you see
method $foo @args;
or
$foo->method(@args);
you can't be sure whether it's a class method or an instance method being
called, since $foo could be an object OR the name of a class.
And they're both defined the same way, as a normal function.
The only REAL difference is that a class method expects its first argument
to be the name of a class, and an instance method expects its first
argument to be an object.
Here's a brief example; you should follow this up with the documentation
already suggested to you.
package Foo;
my @instances;
sub new {
my $class = shift;
my $obj = bless { count => scalar(@instances) }, $class;
push @instances, $obj;
return $obj;
}
sub get_count {
my $self = shift;
return $self->{count};
}
sub get_instance {
my ($class, $idx) = @_;
# we don't really USE $class,
# so this can be called by objects OR classes
return $instances[$idx];
}
sub all_instances {
my $class = shift;
# same here, we don't really NEED the argument we're passed
return @instances;
}
This class could be used in the following way:
use Foo;
my $first = Foo->new; # $first's count is 0
my $second = Foo->new; # $second's count is 1
my $third = Foo->new; # $third's count is 2
print $second->get_count; # 1
print Foo->get_instance(2)->get_count; # 2, but we already knew that
# these two return the SAME list of objects
my @objs = Foo->all_instances;
my @same = $second->all_instances;
Although I don't see it done often, you can write a function that behaves
different if it receives a class rather than an object:
sub get_count {
my $self = shift;
# if it was $obj->get_count(), return $obj's count
return $self->{count} if ref $self;
# otherwise, return the requested object
return $instances[shift];
}
The two ways to call this are:
# returns the object held in $third
my $specific_instance = Foo->get_count(2);
# returns 1, the count of $second
my $c = $second->get_count;
I wouldn't recommend this practice, though, because it can be difficult to
tell what's going on. I would suggest having separate names of class
methods and instance methods.
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]
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