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Home: Perl Programming Help: Beginner:
[solved] Problem to call an object method on objects collected in an arry

framp
Novice

Apr 10, 2009, 4:24 AM

Post #1 of 6 (692 views)

[solved] Problem to call an object method on objects collected in an arry	Can't Post

Hi,

I'm new in the world of Perl - but not in the world of programming languages and OO Wink

. I want to rewrite a huge bash script and use OO Perl to learn and practice Perl. I already created a lot of OO Perl sample code to get familiar with Perl and now I'm struggling with a weired problem.

I have a collection of objects in an arry and want to loop over the collection of objects and call a method on all objects.

It works when I use a plain array. When I use Class::Std (as suggested by Conway in his Best Practices) to encapsulate the object data of my class I get

Code

Can't call method "collect" on unblessed reference at

.

That's the code which works:

Code

my $ic1 = InterfaceCollector->new( { name => "IfCollector1" } ); 
my $ic2 = InterfaceCollector->new( { name => "IfCollector2" } ); 
 
$ic1->collect(); # explicit method call 
$ic2->collect(); 
 
my @collectorList; 
push @collectorList, $ic1; 
push @collectorList, $ic2; 
 
foreach my $collector ( @collectorList ) { # method call to all objects in collection 
	$collector->collect(); 
}

That's the code which doesn't work:

Code

package NwDataCollector; 
use Class::Std; 
use Data::Dumper; 
 
{ 
	my %name : ATTR( : name      => 'name' ); 
	my %collectorList : ATTR( : get => 'collectorList' ); 
 
	sub BUILD { 
		my ( $self, $ident, $arg_ref ) = @_; 
		$collectorList{ ident $self} = (); 
		print "*** colletcorList after initialization\n"; 
		print Data::Dumper->Dump([$collectorList{ident $self}]);		 
		return; 
	} 
 
	sub run { 
		my ($self) = @_; 
		print "*** " . $self->get_name() . " started ***\n"; 
		foreach my $collector ( $self->get_collectorList() ) { 
			$collector->collect(); # <----- boom, unblessed reference 
		} 
	} 
 
	sub add_collector { 
		my ( $self, $collector ) = @_; 
		print "Adding " . $collector->get_name() . "\n"; 
		push @{$collectorList{ident $self}}, $collector; 
#		push @{$self->get_collectorList()},$collector; 
		print "*** collectorList in add_collector\n"; 
		print Data::Dumper->Dump($collectorList{ident $self});		 
	} 
 
}

"Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect." Linus Benedict Torvalds, 28.9.2003

(This post was edited by framp on Apr 11, 2009, 12:23 AM)

Tumata
User

Apr 10, 2009, 4:55 AM

Post #2 of 6 (687 views)

Re: [framp] Problem to call an object method on objects collected in an arry [In reply to]	Can't Post

As I understand Object in Perl is a scalar and associated with it methods. Typically scalar is hash reference. And process of associations is performed by bless. Defining this scalar and blessing are usually performed in constructor. But I don't see any method which looks like constructor in your code. So, at first you should define such method.

framp
Novice

Apr 10, 2009, 5:05 AM

Post #3 of 6 (684 views)

Re: [Tumata] Problem to call an object method on objects collected in an arry [In reply to]	Can't Post

Thank you very much Tumata for your reply.

Class::Std requires to define a sub BUILD which is called under the cover when a ctor is called for a class. So the following code is the actual ctor:

Code

my ( $self, $ident, $arg_ref ) = @_;  
		$collectorList{ ident $self} = ();  
		print "*** colletcorList after initialization\n";  
		print Data::Dumper->Dump([$collectorList{ident $self}]);		  
		return;

See http://search.cpan.org/~dmuey/Class-Std-0.0.9/lib/Class/Std.pm for details.

I added a Dumper statement just before the foreach loop and get

Code

$VAR1 = bless( do{\(my $o = undef)}, 'InterfaceCollector' ); 
$VAR2 = bless( do{\(my $o = undef)}, 'InterfaceCollector' );

so the collectorList is filled with InterfaceCollectors and should be able to accept 'collect' calls.

"Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect." Linus Benedict Torvalds, 28.9.2003

(This post was edited by framp on Apr 10, 2009, 5:21 AM)

framp
Novice

Apr 10, 2009, 5:37 AM

Post #4 of 6 (680 views)

Re: [framp] Problem to call an object method on objects collected in an arry [In reply to]	Can't Post

I dumped the $collector variable with Dumper and found out that it's actually still the collectList array - and not the element of the list Crazy

.
Then I changed the code to

Code

	sub run { 
		my ($self) = @_; 
		print "*** " . $self->get_name() . " started ***\n"; 
		print Data::Dumper->Dump($collectorList{ident $self});		 
#		foreach my $collector ( $self->get_collectorList() ) { 
		foreach my $collector ( @{$self->get_collectorList()} ) { 
			print "##############\n"; 
			print Data::Dumper->Dump([$collector]);				 
			$collector->collect(); 
		} 
	}

and it works now. I now found the solution - but I don't understand why I have to cast to an array ...

"Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect." Linus Benedict Torvalds, 28.9.2003

(This post was edited by framp on Apr 10, 2009, 5:38 AM)

framp
Novice

Apr 11, 2009, 12:22 AM

Post #5 of 6 (661 views)

Re: [framp] Problem to call an object method on objects collected in an arry [In reply to]	Can't Post

Looks like I found out why the original array is returned by the autogenerated getter method: THe getter just returns the pointer to the array and that's why it has to be casted. Therefore I created another method

Code

	sub getCollectorList { 
		my ( $self, $collector ) = @_; 
		return @{$collectorList{ident $self}}; 
	}

which hides the array cast and removed the generated getter.

I started to read docs about Moose which looks much better than Class::Std. Moose has for example a modifier which forces the created getter to cast the return value to the right type Smile

KevinR
Veteran

Apr 11, 2009, 12:26 AM

Post #6 of 6 (659 views)

Re: [framp] Problem to call an object method on objects collected in an arry [In reply to]	Can't Post

This is supposed to be a much better module than the one you are using:

http://search.cpan.org/~jdhedden/Object-InsideOut-3.54/lib/Object/InsideOut.pod

I say "supposed" because I have never used either and I am relying on the opinion of other experienced perl people that it is better. Take a look at it if interested.
-------------------------------------------------

(This post was edited by KevinR on Apr 11, 2009, 12:27 AM)

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