I get an error message while trying to access $self and other variables in a sub inside an object. When the sub is called from outside the object everything works fine. But when I try to access it within the object I get an error (see below).
Here is an example code describing my problem:
package input;
use warnings;
use strict;
sub new {
my $class = shift;
my $self = { };
$self->{_name} = shift;
bless ($self, $class);
return $self;
}
sub test1{
my $self = shift;
my $person = shift;
return $self->{_name}." and ".$person;
}
sub test2{
my $self = shift;
my $person = shift;
print test1($self,$person);
}
package Main;
use warnings;
use strict;
my $i = input->new("Jon");
print $i->test1("Me")."\n";
$i->test2();
The call for print $i->test1("Me")."\n"; does work fine.
I like to access test1() within a different function inside the object.
But for $i->test2(); I get the error
Use of uninitiated value $person in concatenation (.) or String at Line 22.
If I would write
sub test2{
my $self = shift;
my $person = "Jim";
print test1($self,$person);
}
It would work, too.
But I explicitly want to pass some other Variables to the sub besides $self. Since I want to use $self and the other variables. I think it has something to do with passing $self to the sub or not, but I can't figure out how to access $self without the my $self = shift; command.
Use of uninitiated value $person in concatenation (.) or String at Line 22.
When calling test2 method you've forgot $person argument, ie.
$i->test2();
should be
$i->test2("Someone");
Related
This is my first time using OOP with perl. I am in the processes of refactoring a 4k line procedural program at work. It seems pretty straight forward but I am having an issue with inheritance and SUPER.
Error message:
"Can't locate object method "New" via package "Module::SUPER" at Module.pm line 10"
I have tried, use base, parent and setting #ISA but they all get the same error. I'm sure I have to be overlooking something.
(This is not code from the program I am working on. Just an example that produces the same error)
All .pm and .pl files are in the same directory in this example. In the program I am working on the main program is in bin and the modules will be in ../modules(relative to bin).
I would assume this would be all I need to make that work:
use lib "../modules";
If I am wrong in thinking that please let me know.
Parent Module
package BaseModule;
use strict;
use warnings;
sub new {
my $class = shift;
my $self = {
ARRAY => shift,
DIVIDER => ","
};
bless ($self, $class);
return $self;
}
sub array {
my $self = shift;
if(#_) { $self->{ARRAY} = shift };
return $self->{ARRAY};
}
sub divider {
my $self = shift;
if(#_) { $self->{DIVIDER} = shift };
return $self->{DIVIDER};
}
sub testSub {
my $self = shift;
print join($self->{DIVIDER}, #{ $self->{ARRAY} } );
return 1;
}
1;
Child Module
package Module;
use strict;
use warnings;
#use base qw(BaseModule);
#require BaseModule;
#our #ISA = qw(BaseModule);
use parent qw(BaseModule);
sub new {
my $class = shift;
my $self = $class->SUPER::New(#_);
$self->{STRING} = shift;
bless ($self, $class);
return $self;
}
sub string {
my $self = shift;
if(#_) { $self->{STRING} = shift };
return $self->{STRING};
}
sub testSub {
my $self = shift;
print "$self->{STRING}:\n";
$self->SUPER::testSub();
return 1;
}
1;
Do I need to bless the child class if the parent class returns an already blessed $self?
Main Script
#!/usr/bin/perl
use strict;
use warnings;
use Module;
my $module = Module->new([1, 2, 3, 4, 5], "Example");
$module->divider(" | "); # Test Changing divider;
$module->testSub();
Any help is greatly appreciated.
"Can't locate object method "New" via package "Module::SUPER" at Module.pm line 10"
You try to call BaseModule::New whis hasn't been defined (did you mean BaseModule::new? Perl is case sensitive).
Do I need to bless the child class if the parent class returns an
already blessed $self?
No, $self at that point is already blesses (you could check that by means of Scalar::Util::blessed().
I have a base class which calls a method which is overridden in a child class, in Perl. Currently, it still calls the base class version of the method, but I want it to call the base if there is one. Here is a simplified rendition of my code:
package Test;
use strict;
use warnings;
sub Main
{
my $self = shift;
return $self->SomeFunc();
}
sub SomeFunc
{
my $self = shift;
#...
return 1;
}
package Test2;
use strict;
use warnings;
use base qw(Test);
sub SomeFunc
{
my $self = shift;
#...
return 0;
}
package main;
use Test2;
my $test = new Test2();
print $test->Main();
and I am getting a 1 when I run this!
PS my apologies, I'm not used to creating examples in working perl code, please forgive the obvious errors.
The problem would be in your constructor, but you don't have one so your code doesn't even do what you say it does
You have probably written something like
sub new {
bless {};
}
which blesses an empty hash into the current package. Instead you need to take the class name from the first parameter passed to the constructor, like this
You should also avoid using capital letters in your lexical identifiers as they are reserved for global identifiers like package names. If you must use CamelCase then at least makeSureTheFirstLetterIsLowerCase. The standard for both Perl and Python is to use the much_clearer_snake_case
Test.pm
package Test;
use strict;
use warnings;
sub new {
my $class = shift;
bless {}, $class;
}
sub main {
my $self = shift;
$self->some_func();
}
sub some_func {
my $self = shift;
'Test::some_func';
}
Test2.pm
package Test2;
use strict;
use warnings;
use parent 'Test';
sub some_func {
my $self = shift;
'Test2::some_func';
}
main.pl
use strict;
use warnings;
my $test = Test->new;
print $test->main, "\n";
$test = Test2->new;
print $test->main, "\n";
output
Test::some_func
Test2::some_func
new doesn't mean anything in perl unless you make a function with that method name.
You need to bless an object
You can either directly bless an object
my $test = { };
bless $test, "Test2";
or make a new method that does the blessing for you:
sub new{
my $class = shift;
my $test = { };
bless $test, $class;
}
I am new to OO perl. I am trying to write one simple program but getting the error.
Created a package Employee.pm as
package Employee;
sub new {
my $class = shift;
my $self = {};
bless $self, $class;
return $self;
}
sub get_names {
my $self = #_;
print " getting the names \n";
return $self;
}
sub set_names {
my ($self, $last_name) = #_;
$self->{last_name} = $last_name;
return $self->{$last_name};
}
1;
And created a .pl file as
use strict;
use warnings;
use Employee;
my $obj = new Employee("name" => "nitesh", "last_name" => "Goyal");
my $val = $obj->get_names();
print %$val;
my $setName = $obj->set_names("kumar");
print "$setName \n";
I am getting error as
"Can't use string ("1") as a HASH ref while "strict refs" in use at class1.txt line 10."
The error
"Can't use string ("1") as a HASH ref ..
Comes from this part:
sub get_names {
my $self = #_;
When an array is put in scalar context, it returns its size. Since you call the sub with
$obj->get_names();
Only one argument is passed, which is the object, so #_ contains 1 argument, and its size is 1, therefore in the sub get_names, the variable $self is set to 1. Hence the error. What you probably should do is
my $self = shift;
But then, that will not do anything, because you never stored the names in your constructor. As mpapec said, you should do
my $self = { #_ };
in the constructor sub new.
Also, in get_names, you simply return the object, which is not very useful. You should perhaps return $self->{name} and $self->{last_name}.
There is a following class:
package MyClass;
use strict;
use warnings;
sub new
{
my $class = shift();
my $self = {
_class_member => "default"
};
bless ($self, $class);
return $self;
}
How can I set/get the value of the _class_member?
I tried the following code:
sub set_name
{
my $self = shift();
$self->_class_member = shift();
}
But I get the following error:
Can't locate object method "_class_member" via package "MyClass" ...
What am I doing wrong here?
$self is a blessed hash. Unless the you or the original author provided the method _class_member, there's no such method.
You can however, "reach in" the hash to access it:
$self->{'_class_member'} = shift;
This is not a recommended practice for instance values because it's just as easy to type:
$self->{'_vlass_member'} = shift;
without a complaint. Hence the value of accessors.
Currently I am making a new module and I was wondering how could I implement in my module 2 things.
We often see the use like:
use My::Module qw(something);
for example:
use CGI::Carp qw(fatalsToBrowser);
So the first question is, how do i
retrieve this, i mean wether the
user has specified anything and what
he specified ?
Second question is, How do i pass and read the args
directly on the constructor like
this:
my $my_module = My::Module->new(arg1,arg2,arg3);
AS requested on the comment the simple module test code:
package My::Module;
# $Id$
use strict;
use Carp;
sub new {
my $class = shift;
my $self = {};
$self->{ARG1} = undef;
$self->{ARG2} = undef;
$self->{ARG3} = undef;
$self->{ARG4} = undef;
bless($self,$class);
return $self;
}
sub arg1 {
my $self = shift;
if (#_) { $self->{ARG1} = shift }
return $self->{ARG1};
}
sub arg2 {
my $self = shift;
if (#_) { $self->{ARG2} = shift }
return $self->{ARG2};
}
sub arg3 {
my $self = shift;
if (#_) { $self->{ARG3} = shift }
return $self->{ARG3};
}
sub arg4 {
my $self = shift;
if (#_) { $self->{ARG4} = shift }
return $self->{ARG4};
}
sub dump {
my $self = shift;
require Data::Dumper;
my $d = Data::Dumper->new([$self], [ref $self]);
$d->Deepcopy(1);
return $d->Dump();
}
1; # so the require or use succeeds
perldoc -f use explains that the use keyword is simply loading a module during compile-time, and then calling ->import on it. The arguments a caller gave to the use statement will be passed to the import method call.
As for your second question: constructors are just methods. Getting their arguments works like it does for any other method or function, using the #_ variable.
import subroutine gets the arguments passed in a use. The following code samples should help you.
File: My/Module.pm
package My::Module;
use warnings;
use strict;
use Data::Dumper;
sub import {
my ( $package, #args ) = #_;
print Dumper \#args;
}
1;
File: module.pl
#!/usr/bin/env perl
use warnings;
use strict;
use My::Module qw(something);
If you are programming an object oriented module, you may try Moose which will save you lots of time.