162 lines
4.9 KiB
RPMSpec
162 lines
4.9 KiB
RPMSpec
#
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# spec file for package perl-Class-Null
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#
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# Copyright (c) 2024 SUSE LLC
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#
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# All modifications and additions to the file contributed by third parties
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# remain the property of their copyright owners, unless otherwise agreed
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# upon. The license for this file, and modifications and additions to the
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# file, is the same license as for the pristine package itself (unless the
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# license for the pristine package is not an Open Source License, in which
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# case the license is the MIT License). An "Open Source License" is a
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# license that conforms to the Open Source Definition (Version 1.9)
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# published by the Open Source Initiative.
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# Please submit bugfixes or comments via https://bugs.opensuse.org/
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#
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%define cpan_name Class-Null
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Name: perl-Class-Null
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Version: 2.110.730
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Release: 0
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%define cpan_version 2.110730
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License: Artistic-1.0 OR GPL-1.0-or-later
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Summary: Implements the Null Class design pattern
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URL: https://metacpan.org/release/%{cpan_name}
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Source0: https://cpan.metacpan.org/authors/id/M/MA/MARCEL/%{cpan_name}-%{cpan_version}.tar.gz
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Source100: README.md
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BuildArch: noarch
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BuildRequires: perl
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BuildRequires: perl-macros
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BuildRequires: perl(ExtUtils::MakeMaker) >= 6.31
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BuildRequires: perl(Test::More) >= 0.94
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Provides: perl(Class::Null) = %{version}
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%undefine __perllib_provides
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%{perl_requires}
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%description
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This class implements the Null Class design pattern.
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Suppose that methods in your object want to write log messages to a log
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object. The log object is possibly stored in a slot in your object and can
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be accessed using an accessor method:
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package MyObject;
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use base 'Class::Accessor';
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__PACKAGE__->mk_accessors(qw(log));
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sub do_it {
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my $self = shift;
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$self->log->log(level => 'debug', message => 'starting to do it');
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...
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$self->log->log(level => 'debug', message => 'still doing it');
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...
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$self->log->log(level => 'debug', message => 'finished doing it');
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}
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The log object simply needs to have a 'log()' method that accepts two named
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parameters. Any class defining such a method will do, and 'Log::Dispatch'
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fulfills that requirement while providing a lot of flexibility and
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reusability in handling the logged messages.
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You might want to log messages to a file:
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use Log::Dispatch;
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my $dispatcher = Log::Dispatch->new;
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$dispatcher->add(Log::Dispatch::File->new(
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name => 'file1',
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min_level => 'debug',
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filename => 'logfile'));
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my $obj = MyObject->new(log => $dispatcher);
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$obj->do_it;
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But what happens if we don't define a log object? Your object's methods
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would have to check whether a log object is defined before calling the
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'log()' method. This leads to lots of unwieldy code like
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sub do_it {
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my $self = shift;
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if (defined (my $log = $self->log)) {
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$log->log(level => 'debug', message => 'starting to do it');
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}
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...
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if (defined (my $log = $self->log)) {
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$log->log(level => 'debug', message => 'still doing it');
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}
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...
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if (defined (my $log = $self->log)) {
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$log->log(level => 'debug', message => 'finished doing it');
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}
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}
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The proliferation of if-statements really distracts from the actual call to
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'log()' and also distracts from the rest of the method code. There is a
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better way. We can ensure that there is always a log object that we can
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call 'log()' on, even if it doesn't do very much (or in fact, anything at
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all).
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This object with null functionality is what is called a null object. We can
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create the object the usual way, using the 'new()' constructor, and call
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any method on it, and all methods will do the same - nothing. (Actually, it
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always returns the same 'Class::Null' singleton object, enabling method
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chaining.) It's effectively a catch-all object. We can use this class with
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our own object like this:
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package MyObject;
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use Class::Null;
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# some class constructor and accessor declaration here
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sub init {
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my $self = shift;
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...
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$self->log(Class::Null->new);
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...
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}
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sub do_it {
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my $self = shift;
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$self->log->log(level => 'debug', message => 'starting to do it');
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...
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$self->log->log(level => 'debug', message => 'still doing it');
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...
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$self->log->log(level => 'debug', message => 'finished doing it');
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}
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This is only one example of using a null class, but it can be used whenever
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you want to make an optional helper object into a mandatory helper object,
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thereby avoiding unnecessarily complicated checks and preserving the
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transparency of how your objects are related to each other and how they
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call each other.
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Although 'Class::Null' is exceedingly simple it has been made into a
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distribution and put on CPAN to avoid further clutter and repetitive
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definitions.
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%prep
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%autosetup -n %{cpan_name}-%{cpan_version}
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%build
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perl Makefile.PL INSTALLDIRS=vendor
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%make_build
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%check
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make test
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%install
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%perl_make_install
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%perl_process_packlist
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%perl_gen_filelist
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%files -f %{name}.files
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%doc Changes README
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%license LICENSE
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%changelog
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