OO in perl
Perl Object Oriented Programming is very confusing (to me at least :)
---
package Test;
sub new {}
sub f_one{}
sub f_two{}
1;
---
I can call using
my $test = Test-new-f_one;
But why this not works?
my $test = Test-new-f_one-f_two;
--
--beast
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
RE: OO in perl
Beast [EMAIL PROTECTED] asked: I can call using my $test = Test-new-f_one; Test-new returns an object of type Test; and so your code is equivalent to my $obj = Test-new; my $test = $obj-f_one; But why this not works? my $test = Test-new-f_one-f_two; This will work if f_one returns a valid Test object. HTH, Thomas -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: OO in perl
On Jul 19, Beast said:
package Test;
sub new {}
sub f_one{}
sub f_two{}
You've neglected to show us the contents. I'll assume that new() creates
and returns an object. I'll also assume that f_one() and f_two() DO NOT
return objects.
my $test = Test-new-f_one;
Test-new returns an object, which then has its f_one() method called.
But why this not works?
my $test = Test-new-f_one-f_two;
Because f_one() does not return an object!
--
Jeff japhy Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
http://japhy.perlmonk.org/ % have long ago been overpaid?
http://www.perlmonks.org/ %-- Meister Eckhart
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
Re: Attempting OO with Perl - New() method in subclass not working
Brad == Brad Carlson [EMAIL PROTECTED] writes:
Brad Just to clarify, the only reason I don't need a new() method in the
Brad subclass is because any class-specific logic is contained in the _init()
Brad method for both parent and subclass. If there were no _init() method,
Brad then both classes would have a new(), right?
Yes. You can either put your per-class initialization into -new,
and use SUPER::new for parent classes, or have an _init, which your
most-parent-class must remember to call. The latter is a Smalltalk-ish
standard, where Object class[1] has something like:
new
^self basicNew initialize
and initialize[2] looks like
initialize
^self
Then every derived class that wants additional hooks does:
initialize
super initialize.
my code here.
^self
In Perl terms, this would look like:
sub new {
my $class = shift;
my $self = bless [EMAIL PROTECTED], $class;
return $self-initialize; # and return this
}
sub initialize { # base definition
my $self = shift;
return $self;
}
sub initialize { # derived definition
my $self = shift;
$self-SUPER::initialize;
$self-{extra} = thing;
return $self;
}
By the way, I really really recommend that people who are doing
serious OO get some Smalltalk experience. Smalltalk got a *lot*
of things right. Free implementations of Smalltalk for all platforms
are available at www.squeak.org, and there's a wealth of both free
and commercial publications about learning Smalltalk.
[1] Actually, it's in Behavior class.
[2] Defined in ProtoObject, the base class for Object
--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
merlyn@stonehenge.com URL:http://www.stonehenge.com/merlyn/
Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
Re: Attempting OO with Perl - New() method in subclass not working
Jeff == Jeff 'japhy' Pinyan [EMAIL PROTECTED] writes:
Jeffsub new {
Jeff my $that = shift;
Jeff my $class = ref($that) || $that;
Jeff my $self = $class-SUPER::new();
Jeff $self-SUPER::_init();
There's a rule of thumb from smalltalk that if you're using a super
call with a method name other than your own, you just broke something.
And you just broke something.
The problem is not here. The problem is in _init, which also
needs to call SUPER::_init. And then the rule correctly points
out the solution. How nice.
Jeff return $self;
Jeff}
--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
merlyn@stonehenge.com URL:http://www.stonehenge.com/merlyn/
Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
Re: Attempting OO with Perl - New() method in subclass not working
On Apr 1, Randal L. Schwartz said:
Jeff == Jeff 'japhy' Pinyan [EMAIL PROTECTED] writes:
Jeffsub new {
Jeff my $that = shift;
Jeff my $class = ref($that) || $that;
Jeff my $self = $class-SUPER::new();
Jeff $self-SUPER::_init();
There's a rule of thumb from smalltalk that if you're using a super
call with a method name other than your own, you just broke something.
And you just broke something.
The problem is not here. The problem is in _init, which also
needs to call SUPER::_init. And then the rule correctly points
out the solution. How nice.
Oh, right. April Fool? ;)
--
Jeff japhy Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
http://japhy.perlmonk.org/ % have long ago been overpaid?
http://www.perlmonks.org/ %-- Meister Eckhart
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
Re: Attempting OO with Perl - New() method in subclass not working
Jeff == Jeff 'japhy' Pinyan [EMAIL PROTECTED] writes: Jeff Oh, right. April Fool? ;) Perhaps that's half right. :) -- Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095 merlyn@stonehenge.com URL:http://www.stonehenge.com/merlyn/ Perl/Unix/security consulting, Technical writing, Comedy, etc. etc. See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training! -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
RE: Attempting OO with Perl - New() method in subclass not working
Thank you!
I tried the SUPER-_init() and that took care of it. However, I donn't
want to force an inherited class to have to know how the parent's new()
works, so I tried this as well (and it worked) - I have the new() call
it's own _init explicitly:
# the new() from Logon.pm
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = $class-SUPER::new();
$self-Logon::_init();
return $self;
}
# the new() from DBLogon.pm
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = $class-SUPER::new();
$self-DBLogon::_init();
return $self;
}
Thanks again, I've been fighting this for quite a while.
-Original Message-
From: Jeff 'japhy' Pinyan [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 31, 2005 7:18 PM
To: [EMAIL PROTECTED]
Cc: beginners@perl.org
Subject: Re: Attempting OO with Perl - New() method in subclass not
working
On Mar 31, [EMAIL PROTECTED] said:
When I try to assign values to the DBLogon object's attributes, I get
the following error: Can't access 'USERID' field in object of class
DBLogon at testdblogon.pl line 7. What am I missing?
The problem is that Logon's new() method is calling LogonDB's _init()
method. To get around that, you'll have to do:
package DBLogon;
use Logon;
@ISA = qw (Logon);
use Carp;
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = $class-SUPER::new();
$self-SUPER::_init();
return $self;
}
--
Jeff japhy Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
http://japhy.perlmonk.org/ % have long ago been overpaid?
http://www.perlmonks.org/ %-- Meister Eckhart
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
RE: Attempting OO with Perl - New() method in subclass not workin g
[EMAIL PROTECTED] wrote: I am trying to build an inheritable object, and I am using examples from the Perl Cookbook, 2nd edition, mostly Recipe 13.1, using the new and _init methods. Your subclass does not need (and should not have) a new() method; it can use the one from the base class. As Randal pointed out, the subclass _init needs to call $self-SUPER::_init(), and then do any additional initialization. If there is no additional initialization in the subclass, you don't need an _init method there either. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
RE: Attempting OO with Perl - New() method in subclass not working
Okay, why is the subclass's new() not required? Is it because the
DBLogon's additional field (DBNAME) is added via the _init() method? So
you end up with something like this:
# Base class Logon new()
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = {};
bless $self, $class;
$self-_init();
return $self;
}
# Base class Logon _init()
sub _init {
my $self = shift;
$self-{USERID} = undef;
$self-{SERVER} = undef;
}
Then the subclass DBLogon would no longer have a new() method, but would
retain its _init() method, which would be modified to call the SUPER's
_init as well, right?
# Subclass DBLogon init()
sub _init {
my $self = shift;
$self-SUPER::_init();
$self-{DBNAME} = undef;
}
Just to clarify, the only reason I don't need a new() method in the
subclass is because any class-specific logic is contained in the _init()
method for both parent and subclass. If there were no _init() method,
then both classes would have a new(), right?
-Original Message-
From: Bob Showalter [mailto:[EMAIL PROTECTED]
Sent: Friday, April 01, 2005 10:44 AM
To: '[EMAIL PROTECTED]'; beginners@perl.org
Subject: RE: Attempting OO with Perl - New() method in subclass not
working
[EMAIL PROTECTED] wrote:
I am trying to build an inheritable object, and I am using examples
from the Perl Cookbook, 2nd edition, mostly Recipe 13.1, using the new
and _init methods.
Your subclass does not need (and should not have) a new() method; it can
use the one from the base class.
As Randal pointed out, the subclass _init needs to call
$self-SUPER::_init(), and then do any additional initialization. If
there is no additional initialization in the subclass, you don't need an
_init method there either.
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
Attempting OO with Perl - New() method in subclass not working
I am trying to build an inheritable object, and I am using examples from
the Perl Cookbook, 2nd edition, mostly Recipe 13.1, using the new and
_init methods.
I created a base class Logon and a subclass called DBLogon, in files
Logon.pm and DBLogon.pm, respectively. All referenced files are copied
below. I can create a Logon object and print its contents with no
problem (see test program testlogon.pl). However, my subclass is not
working. According to Recipe 13.1 in the cookbook, have an _init()
function called by new() can make the class more inheritable (separate
the memory allocation and blessing step from the instance data
initialization step, p. 507-508).
When I try to assign values to the DBLogon object's attributes, I get
the following error: Can't access 'USERID' field in object of class
DBLogon at testdblogon.pl line 7. What am I missing?
# Logon.pm
package Logon;
use Carp;
# Constructor
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = {};
bless $self, $class;
$self-_init();
return $self;
}
sub _init {
my $self = shift;
$self-{USERID} = undef;
$self-{SERVER} = undef;
}
sub display {
my $self = shift;
my @keys;
if (@_ == 0) {
@keys = sort keys (%$self);
} else {
@keys = @_;
}
foreach $key (@keys) {
$key = uc $key;
my $label = ucfirst lc $key;
print $label: $self-{$key}\n;
}
}
sub userid;
sub server;
sub AUTOLOAD {
my $self = shift;
my $type = ref($self) || croak $self is not an object;
my $name = uc $AUTOLOAD;
$name =~ s/.*://; # Strip fully-qualified portion
unless ( exists $self-{$name} ) {
croak Can't access '$name' field in object of class
$type;
}
if (@_) {
return $self-{$name} = shift;
} else {
return $self-{$name};
}
}
1;
# DBLogon.pm
package DBLogon;
use Logon;
@ISA = qw (Logon);
use Carp;
# Constructor
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = $class-SUPER::new();
bless $self, $class;
$self-_init();
return $self;
}
sub _init {
my $self = shift;
$self-{DBNAME} = undef;
}
1;
There are also 2 test programs, testlogon.pm and testdblogon.pm:
# Logon.pm
#!/usr/bin/perl
use DBLogon;
my $mylogon = DBLogon-new();
$mylogon-userid(user1);
$mylogon-server(server1);
$mylogon-dbname(db1);
$mylogon-display();
# Logon.pm
#!/usr/bin/perl
use DBLogon;
my $mylogon = DBLogon-new();
$mylogon-userid(user1);
$mylogon-server(server1);
$mylogon-dbname(db1);
$mylogon-display();
Re: Attempting OO with Perl - New() method in subclass not working
On Mar 31, [EMAIL PROTECTED] said:
When I try to assign values to the DBLogon object's attributes, I get
the following error: Can't access 'USERID' field in object of class
DBLogon at testdblogon.pl line 7. What am I missing?
The problem is that Logon's new() method is calling LogonDB's _init()
method. To get around that, you'll have to do:
package DBLogon;
use Logon;
@ISA = qw (Logon);
use Carp;
sub new {
my $that = shift;
my $class = ref($that) || $that;
my $self = $class-SUPER::new();
$self-SUPER::_init();
return $self;
}
--
Jeff japhy Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
http://japhy.perlmonk.org/ % have long ago been overpaid?
http://www.perlmonks.org/ %-- Meister Eckhart
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/ http://learn.perl.org/first-response
