Class::Tiny(3pm) User Contributed Perl Documentation Class::Tiny(3pm)NAMEClass::Tiny - Minimalist class construction
VERSION
version 1.006
SYNOPSIS
In Person.pm:
package Person;
use Class::Tiny qw( name );
1;
In Employee.pm:
package Employee;
use parent 'Person';
use Class::Tiny qw( ssn ), {
timestamp => sub { time } # attribute with default
};
1;
In example.pl:
use Employee;
my $obj = Employee->new( name => "Larry", ssn => "111-22-3333" );
# unknown attributes are ignored
my $obj = Employee->new( name => "Larry", OS => "Linux" );
# $obj->{OS} does not exist
DESCRIPTION
This module offers a minimalist class construction kit in around 120
lines of code. Here is a list of features:
· defines attributes via import arguments
· generates read-write accessors
· supports lazy attribute defaults
· supports custom accessors
· superclass provides a standard "new" constructor
· "new" takes a hash reference or list of key/value pairs
· "new" supports providing "BUILDARGS" to customize constructor
options
· "new" calls "BUILD" for each class from parent to child
· superclass provides a "DESTROY" method
· "DESTROY" calls "DEMOLISH" for each class from child to parent
Multiple-inheritance is possible, with superclass order determined via
mro::get_linear_isa.
It uses no non-core modules for any recent Perl. On Perls older than
v5.10 it requires MRO::Compat. On Perls older than v5.14, it requires
Devel::GlobalDestruction.
USAGE
Defining attributes
Define attributes as a list of import arguments:
package Foo::Bar;
use Class::Tiny qw(
name
id
height
weight
);
For each attribute, a read-write accessor is created unless a
subroutine of that name already exists:
$obj->name; # getter
$obj->name( "John Doe" ); # setter
Attribute names must be valid subroutine identifiers or an exception
will be thrown.
You can specify lazy defaults by defining attributes with a hash
reference. Keys define attribute names and values are constants or
code references that will be evaluated when the attribute is first
accessed if no value has been set. The object is passed as an argument
to a code reference.
package Foo::WithDefaults;
use Class::Tiny qw/name id/, {
title => 'Peon',
skills => sub { [] },
hire_date => sub { $_[0]->_build_hire_date },
};
When subclassing, if multiple accessors of the same name exist in
different classes, any default (or lack of default) is determined by
standard method resolution order.
To make your own custom accessors, just pre-declare the method name
before loading Class::Tiny:
package Foo::Bar;
use subs 'id';
use Class::Tiny qw( name id );
sub id { ... }
Even if you pre-declare a method name, you must include it in the
attribute list for Class::Tiny to register it as a valid attribute.
If you set a default for a custom accessor, your accessor will need to
retrieve the default and do something with it:
package Foo::Bar;
use subs 'id';
use Class::Tiny qw( name ), { id => sub { int(rand(2*31)) } };
sub id {
my $self = shift;
if (@_) {
return $self->{id} = shift;
}
elsif ( exists $self->{id} ) {
return $self->{id};
}
else {
my $defaults =
Class::Tiny->get_all_attribute_defaults_for( ref $self );
return $self->{id} = $defaults->{id}->();
}
}
Class::Tiny::Object is your base class
If your class does not already inherit from some class, then
Class::Tiny::Object will be added to your @ISA to provide "new" and
"DESTROY".
If your class does inherit from something, then no additional
inheritance is set up. If the parent subclasses Class::Tiny::Object,
then all is well. If not, then you'll get accessors set up but no
constructor or destructor. Don't do that unless you really have a
special need for it.
Define subclasses as normal. It's best to define them with base,
parent or superclass before defining attributes with Class::Tiny so the
@ISA array is already populated at compile-time:
package Foo::Bar::More;
use parent 'Foo::Bar';
use Class::Tiny qw( shoe_size );
Object construction
If your class inherits from Class::Tiny::Object (as it should if you
followed the advice above), it provides the "new" constructor for you.
Objects can be created with attributes given as a hash reference or as
a list of key/value pairs:
$obj = Foo::Bar->new( name => "David" );
$obj = Foo::Bar->new( { name => "David" } );
If a reference is passed as a single argument, it must be able to be
dereferenced as a hash or an exception is thrown.
Unknown attributes in the constructor arguments will be ignored. Prior
to version 1.000, unknown attributes were an error, but this made it
harder for people to cleanly subclass Class::Tiny classes so this
feature was removed.
You can define a "BUILDARGS" method to change how arguments to new are
handled. It will receive the constructor arguments as they were
provided and must return a hash reference of key/value pairs (or else
throw an exception).
sub BUILDARGS {
my $class = shift;
my $name = shift || "John Doe";
return { name => $name };
};
Foo::Bar->new( "David" );
Foo::Bar->new(); # "John Doe"
Unknown attributes returned from "BUILDARGS" will be ignored.
BUILD
If your class or any superclass defines a "BUILD" method, it will be
called by the constructor from the furthest parent class down to the
child class after the object has been created.
It is passed the constructor arguments as a hash reference. The return
value is ignored. Use "BUILD" for validation, checking required
attributes or setting default values that depend on other attributes.
sub BUILD {
my ($self, $args) = @_;
for my $req ( qw/name age/ ) {
croak "$req attribute required" unless defined $self->$req;
}
croak "Age must be non-negative" if $self->age < 0;
$self->msg( "Hello " . $self->name );
}
The argument reference is a copy, so deleting elements won't affect
data in the original (but changes will be passed to other BUILD methods
in @ISA).
DEMOLISH
Class::Tiny provides a "DESTROY" method. If your class or any
superclass defines a "DEMOLISH" method, they will be called from the
child class to the furthest parent class during object destruction. It
is provided a single boolean argument indicating whether Perl is in
global destruction. Return values and errors are ignored.
sub DEMOLISH {
my ($self, $global_destruct) = @_;
$self->cleanup();
}
Introspection and internals
You can retrieve an unsorted list of valid attributes known to
Class::Tiny for a class and its superclasses with the
"get_all_attributes_for" class method.
my @attrs = Class::Tiny->get_all_attributes_for("Employee");
# returns qw/name ssn timestamp/
Likewise, a hash reference of all valid attributes and default values
(or code references) may be retrieved with the
"get_all_attribute_defaults_for" class method. Any attributes without
a default will be "undef".
my $def = Class::Tiny->get_all_attribute_defaults_for("Employee");
# returns {
# name => undef,
# ssn => undef
# timestamp => $coderef
# }
The "import" method uses two class methods, "prepare_class" and
"create_attributes" to set up the @ISA array and attributes. Anyone
attempting to extend Class::Tiny itself should use these instead of
mocking up a call to "import".
When the first object is created, linearized @ISA, the valid attribute
list and various subroutine references are cached for speed. Ensure
that all inheritance and methods are in place before creating objects.
(You don't want to be changing that once you create objects anyway,
right?)
RATIONALE
Why this instead of Object::Tiny or Class::Accessor or something else?
I wanted something so simple that it could potentially be used by core
Perl modules I help maintain (or hope to write), most of which either
use Class::Struct or roll-their-own OO framework each time.
Object::Tiny and Object::Tiny::RW were close to what I wanted, but
lacking some features I deemed necessary, and their maintainers have an
even more strict philosophy against feature creep than I have.
I also considered Class::Accessor, which has been around a long time
and is heavily used, but it, too, lacked features I wanted and did
things in ways I considered poor design.
I looked for something else on CPAN, but after checking a dozen class
creators I realized I could implement exactly what I wanted faster than
I could search CPAN for something merely sufficient.
In general, compared to most things on CPAN (other than Object::Tiny),
Class::Tiny is smaller in implementation and simpler in API.
Specifically, here is how Class::Tiny ("C::T") compares to Object::Tiny
("O::T") and Class::Accessor ("C::A"):
FEATURE C::T O::T C::A
--------------------------------------------------------------
attributes defined via import yes yes no
read/write accessors yes no yes
lazy attribute defaults yes no no
provides new yes yes yes
provides DESTROY yes no no
new takes either hashref or list yes no (list) no (hash)
Moo(se)-like BUILD/DEMOLISH yes no no
Moo(se)-like BUILDARGS yes no no
no extraneous methods via @ISA yes yes no
Why this instead of Moose or Moo?
Moose and Moo are both excellent OO frameworks. Moose offers a
powerful meta-object protocol (MOP), but is slow to start up and has
about 30 non-core dependencies including XS modules. Moo is faster to
start up and has about 10 pure Perl dependencies but provides no true
MOP, relying instead on its ability to transparently upgrade Moo to
Moose when Moose's full feature set is required.
By contrast, Class::Tiny has no MOP and has zero non-core dependencies
for Perls in the support window. It has far less code, less complexity
and no learning curve. If you don't need or can't afford what Moo or
Moose offer, this is intended to be a reasonable fallback.
That said, Class::Tiny offers Moose-like conventions for things like
"BUILD" and "DEMOLISH" for some minimal interoperability and an easier
upgrade path.
SUPPORT
Bugs / Feature Requests
Please report any bugs or feature requests through the issue tracker at
<https://github.com/dagolden/Class-Tiny/issues>. You will be notified
automatically of any progress on your issue.
Source Code
This is open source software. The code repository is available for
public review and contribution under the terms of the license.
<https://github.com/dagolden/Class-Tiny>
git clone https://github.com/dagolden/Class-Tiny.git
AUTHOR
David Golden <dagolden@cpan.org>
CONTRIBUTORS
· Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
· David Golden <xdg@xdg.me>
· Gelu Lupas <gelu@devnull.ro>
· Karen Etheridge <ether@cpan.org>
· Olivier Mengué <dolmen@cpan.org>
· Toby Inkster <tobyink@cpan.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2013 by David Golden.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
perl v5.22.2 2016-09-14 Class::Tiny(3pm)
