Re: Qn on classes, inheritance, and threads

Williamawalters Tue, 28 Mar 2006 04:59:33 -0800

In a message dated 3/28/2006 5:50:21 A.M. Eastern Standard Time, [EMAIL PROTECTED] writes:

> Hi all,
>
> I have a need to do this (abstracted from the attached working code):
> package BaseClass;
> use threads;
>
> sub doThis
> {
> my $this = shift;
>
> threads->create(\&doThat,$this);

at this point, the compiler is looking for a subroutine doThat in the package

BaseClass and all classes (i.e., packages) that BaseClass derives from.

however, BaseClass derives from nothing; in particular, it does not derive

from DerivedClass, where a subroutine named doThat (or more specifically,

&DerivedClass::doThat) is defined. this is what the error message is saying.

a way around the problem is to say

threads->create(\&DerivedClass::doThat,$this);

> }
>
> package DerivedClass;
> use base 'BaseClass';
>
> sub new
> {
>     my $class = shift;
>     my $this = $class->SUPER::new;
>     return bless $this,$class;
> }
>
> sub doThat
> {
> ...
> }
>
> --- in an app that uses these objects ---
> use DerivedClass;
> my $o = DerivedClass->new;
> $o->doThis;
>
> The error is:
> Undefined subroutine &BaseClass::doThat called at BaseClass.pm
>
> Notice that doThat() is not in the base class, but rather in the
> subclass. Apparently Perl is not able to determine which package to use
> for doThat() within doThis(). I have tried:

perl knows exactly which package (or packages) to use because you have

told it exactly which to use.

>
> threads->create(\&{$this::doThat},$this);
>
> and a few other permutations, but they are all wrong. I'm quite sure
> it's matter of syntax.
>
> I will try to explain myself again if you are confused.
>
> Please advise. Thanks.

hi ji-haw --

consider the following:

-------- begin code ----------------

# t_jhfoo1.pl derived classes 28mar06waw

use strict;
use warnings;

package Foo;

sub foo {
bar();
}

sub bar{
    Bar::drunk();
    printf qq(i am bar in %s \n), __PACKAGE__;
    }

package Bar;
use base 'Foo';

sub drunk {
printf qq(i am drunk in %s \n), __PACKAGE__;
}

package main;

Bar->foo(); # ok: &foo() defined in Bar or in one of its base classes
Foo::foo();
# Bar::foo(); # fails: no &Bar::foo() defined in package Bar
# drunk(); # fails: no &drunk() defined in package main

package Bar;

drunk; # ok

############################

package BaseClass;
use threads;

sub doThis
{
my $this = shift;

# threads->create(\&doThat,$this); # no

# threads->create(\&DerivedClass::doThat,$this); # should work

$this->{_code}->('YES');

}

sub new ($)
{
my ($class) = @_;

    my %hash = (
        _status=>'STOPPED',
        _code => \&DerivedClass::doThat,
        );

return bless \%hash,$class;
}

package DerivedClass;
use base 'BaseClass';

sub new
{
    my $class = shift;
    my $this = $class->SUPER::new;
    return bless $this,$class;
}

sub doThat
{
my ($message) = @_;

print "in doThat: $message \n";
}

# --- in an app that uses these objects ---

package main;

# use DerivedClass;
my $o = DerivedClass->new;
$o->doThis;

------------ end code ----------------

hth -- bill walters

_______________________________________________
ActivePerl mailing list
[email protected]
To unsubscribe: http://listserv.ActiveState.com/mailman/mysubs

Re: Qn on classes, inheritance, and threads

Reply via email to