Doing Nothing
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Doing Nothing Marcel Grünauer (hanekomu) [email protected] Zentraler Informatikdienst der Universität Wien Vienna.pm Tech Meeting, 6th October 2008 Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Central IT Services of the University of Vienna Registry software for the .at zone (also used by .no, .ie, .nl, .au) Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Tatsuhiko Miyagawa “20 modules I haven’t yet talked about”
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Tatsuhiko Miyagawa
10 “20 modules I haven’t yet talked about”
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
➊ Class::Null
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
References may be undef. They need to be checked to ensure they are not undef before invoking any methods on them. This tends to make code less readable. Instead of using an undef reference to convey absence of an object, you use a Null object – an object which implements the expected interface, but whose method body is empty.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
What the hell does that mean?
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
The usual way sub do_it { my $self = shift; if (defined (my $log = $self->log)) { $log->some_method(...); } ... if (defined (my $log = $self->log)) { $log->some_method(...); } ... if (defined (my $log = $self->log)) { $log->some_method(...); } }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
There are three problems.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
(1) The code becomes less readable. Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
(2) You might forget to check definedness. Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
(3) It is boring.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Solution: Class::Null sub init { my $self = shift; $self->log(Class::Null->new); } sub do_it { my $self = shift; $self->log->some_method(...); ... $self->log->some_method(...); ... $self->log->some_method(...); }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
A very efficient way of doing nothing.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Class::Null concept package Class::Null; sub new { our $singleton ||= bless {}, shift } sub AUTOLOAD { our $singleton }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Method Chaining sub AUTOLOAD { our $singleton } sub do_it { my $self = shift; ... $self->log->foo(...)->bar(...)->baz; ... }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Boolean Context sub do_it { my $self = shift; ... if ($self->log->foo(...)) { ... } ... }
The null object returns 0 (a false value) in boolean context.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Class::Null complete package Class::Null; use warnings; use strict; use overload 'bool' '""' '0+' fallback
=> => => =>
sub { 0 }, sub { '' }, sub { 0 }, 1;
sub new { our $singleton ||= bless {}, shift } sub AUTOLOAD { our $singleton }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Questions?
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Thank you! http://search.cpan.org/dist/Class-Null/ http://www.pdfcoke.com/hanekomu http://hanekomu.at/blog
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Central IT Services of the University of Vienna Registry software for the .at zone (also used by .no, .ie, .nl, .au) Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Tatsuhiko Miyagawa “20 modules I haven’t yet talked about”
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Tatsuhiko Miyagawa
10 “20 modules I haven’t yet talked about”
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
➊ Class::Null
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
References may be undef. They need to be checked to ensure they are not undef before invoking any methods on them. This tends to make code less readable. Instead of using an undef reference to convey absence of an object, you use a Null object – an object which implements the expected interface, but whose method body is empty.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
What the hell does that mean?
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
The usual way sub do_it { my $self = shift; if (defined (my $log = $self->log)) { $log->some_method(...); } ... if (defined (my $log = $self->log)) { $log->some_method(...); } ... if (defined (my $log = $self->log)) { $log->some_method(...); } }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
There are three problems.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
(1) The code becomes less readable. Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
(2) You might forget to check definedness. Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
(3) It is boring.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Solution: Class::Null sub init { my $self = shift; $self->log(Class::Null->new); } sub do_it { my $self = shift; $self->log->some_method(...); ... $self->log->some_method(...); ... $self->log->some_method(...); }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
A very efficient way of doing nothing.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Class::Null concept package Class::Null; sub new { our $singleton ||= bless {}, shift } sub AUTOLOAD { our $singleton }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Method Chaining sub AUTOLOAD { our $singleton } sub do_it { my $self = shift; ... $self->log->foo(...)->bar(...)->baz; ... }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Boolean Context sub do_it { my $self = shift; ... if ($self->log->foo(...)) { ... } ... }
The null object returns 0 (a false value) in boolean context.
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Class::Null complete package Class::Null; use warnings; use strict; use overload 'bool' '""' '0+' fallback
=> => => =>
sub { 0 }, sub { '' }, sub { 0 }, 1;
sub new { our $singleton ||= bless {}, shift } sub AUTOLOAD { our $singleton }
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Questions?
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
Thank you! http://search.cpan.org/dist/Class-Null/ http://www.pdfcoke.com/hanekomu http://hanekomu.at/blog
Marcel Grünauer Wednesday, May 27, 2009
Vienna.pm Tech Meeting, 2. Juni 2009
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