File perl-Class-Null.spec of Package perl-Class-Null

Overview Repositories Revisions Requests Users Attributes Meta

File perl-Class-Null.spec of Package perl-Class-Null

#
# spec file for package perl-Class-Null
#
# Copyright (c) 2024 SUSE LLC
#
# All modifications and additions to the file contributed by third parties
# remain the property of their copyright owners, unless otherwise agreed
# upon. The license for this file, and modifications and additions to the
# file, is the same license as for the pristine package itself (unless the
# license for the pristine package is not an Open Source License, in which
# case the license is the MIT License). An "Open Source License" is a
# license that conforms to the Open Source Definition (Version 1.9)
# published by the Open Source Initiative.

# Please submit bugfixes or comments via https://bugs.opensuse.org/
#

%define cpan_name Class-Null
Name:           perl-Class-Null
Version:        2.110.730
Release:        0
%define cpan_version 2.110730
License:        Artistic-1.0 OR GPL-1.0-or-later
Summary:        Implements the Null Class design pattern
URL:            https://metacpan.org/release/%{cpan_name}
Source0:        https://cpan.metacpan.org/authors/id/M/MA/MARCEL/%{cpan_name}-%{cpan_version}.tar.gz
BuildArch:      noarch
BuildRequires:  perl
BuildRequires:  perl-macros
BuildRequires:  perl(ExtUtils::MakeMaker) >= 6.31
BuildRequires:  perl(Test::More) >= 0.94
Provides:       perl(Class::Null) = %{version}
%undefine       __perllib_provides
%{perl_requires}

%description
This class implements the Null Class design pattern.

Suppose that methods in your object want to write log messages to a log
object. The log object is possibly stored in a slot in your object and can
be accessed using an accessor method:

package MyObject;

use base 'Class::Accessor';
  __PACKAGE__->mk_accessors(qw(log));

sub do_it {
    my $self = shift;
    $self->log->log(level => 'debug', message => 'starting to do it');
    ...
    $self->log->log(level => 'debug', message => 'still doing it');
    ...
    $self->log->log(level => 'debug', message => 'finished doing it');
  }

The log object simply needs to have a 'log()' method that accepts two named
parameters. Any class defining such a method will do, and 'Log::Dispatch'
fulfills that requirement while providing a lot of flexibility and
reusability in handling the logged messages.

You might want to log messages to a file:

use Log::Dispatch;

my $dispatcher = Log::Dispatch->new;

$dispatcher->add(Log::Dispatch::File->new(
    name      => 'file1',
    min_level => 'debug',
    filename  => 'logfile'));

my $obj = MyObject->new(log => $dispatcher);
  $obj->do_it;

But what happens if we don't define a log object? Your object's methods
would have to check whether a log object is defined before calling the
'log()' method. This leads to lots of unwieldy code like

sub do_it {
    my $self = shift;
    if (defined (my $log = $self->log)) {
      $log->log(level => 'debug', message => 'starting to do it');
    }
    ...
    if (defined (my $log = $self->log)) {
      $log->log(level => 'debug', message => 'still doing it');
    }
    ...
    if (defined (my $log = $self->log)) {
      $log->log(level => 'debug', message => 'finished doing it');
    }
  }

The proliferation of if-statements really distracts from the actual call to
'log()' and also distracts from the rest of the method code. There is a
better way. We can ensure that there is always a log object that we can
call 'log()' on, even if it doesn't do very much (or in fact, anything at
all).

This object with null functionality is what is called a null object. We can
create the object the usual way, using the 'new()' constructor, and call
any method on it, and all methods will do the same - nothing. (Actually, it
always returns the same 'Class::Null' singleton object, enabling method
chaining.) It's effectively a catch-all object. We can use this class with
our own object like this:

package MyObject;

use Class::Null;

# some class constructor and accessor declaration here

sub init {
    my $self = shift;
    ...
    $self->log(Class::Null->new);
    ...
  }

This is only one example of using a null class, but it can be used whenever
you want to make an optional helper object into a mandatory helper object,
thereby avoiding unnecessarily complicated checks and preserving the
transparency of how your objects are related to each other and how they
call each other.

Although 'Class::Null' is exceedingly simple it has been made into a
distribution and put on CPAN to avoid further clutter and repetitive
definitions.

%prep
%autosetup  -n %{cpan_name}-%{cpan_version}

%build
perl Makefile.PL INSTALLDIRS=vendor
%make_build

%check
make test

%install
%perl_make_install
%perl_process_packlist
%perl_gen_filelist

%files -f %{name}.files
%doc Changes README
%license LICENSE

%changelog

Places

File perl-Class-Null.spec of Package perl-Class-Null

Places