NAME Class::Tiny - Minimalist class construction VERSION version 0.005 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 fatal: eval { Employee->new( name => "Larry", OS => "Linux" ) }; die "Error creating Employee: $@" if $@; DESCRIPTION This module offers a minimalist class construction kit in around 100 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" has heuristics to catch constructor attribute typos * "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 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. 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. Compared to everything else, this is smaller in implementation and simpler in API. (The only API is a list of attributes!) I looked for something like it on CPAN, but after checking a dozen class creators I realized I could implement it exactly how I wanted faster than I could search CPAN for something merely sufficient. Why this instead of Moose or Moo? Moose and Moo are wonderful, but have a lot of dependencies. This doesn't, which makes it great for core or fatpacking. That said, Class::Tiny tries to follow similar conventions for things like "BUILD" and "DEMOLISH" for some minimal interoperability. 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 }, }; 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 { ... } By declaring "id" also with Class::Tiny, you include it in the list of known attributes for introspection. Default values will not be set for custom accessors unless you handle that yourself. 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" ); $obj = Foo::Bar->new( { name => "David" } ); If a reference is passed as a single argument, it must be able to be dereferenced as a hash or an exception is thrown. A shallow copy is made of the reference provided. In order to help catch typos in constructor arguments, any argument that it is not also a valid method (e.g. an accessor or other method) will result in a fatal exception. This is not perfect, but should catch typical transposition typos. Also see "BUILD" for how to explicitly hide non-attribute, non-method arguments if desired. BUILD If your class or any superclass defines a "BUILD" method, it will be called by the constructor from the furthest parent class down to the child class after the object has been created. It is passed the constructor arguments as a hash reference. The return value is ignored. Use "BUILD" for validation or setting default values. sub BUILD { my ($self, $args) = @_; $self->foo(42) unless defined $self->foo; croak "Foo must be non-negative" if $self->foo < 0; } If you want to hide a non-attribute constructor argument from validation, delete it from the passed-in argument hash reference. sub BUILD { my ($self, $args) = @_; if ( delete $args->{do_something_special} ) { ... } } The argument reference is a copy, so deleting elements won't affect data in the object. You have to delete it from both if that's what you want. sub BUILD { my ($self, $args) = @_; if ( delete $args->{do_something_special} ) { delete $self->{do_something_special}; ... } } DEMOLISH Class::Tiny provides a "DESTROY" method. If your class or any superclass defines a "DEMOLISH" method, they will be called from the child class to the furthest parent class during object destruction. It is provided a single boolean argument indicating whether Perl is in global destruction. Return values and errors are ignored. sub DEMOLISH { my ($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"); # @attrs contains qw/name ssn/ 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". SUPPORT Bugs / Feature Requests Please report any bugs or feature requests through the issue tracker at . 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. git clone git://github.com/dagolden/class-tiny.git AUTHOR David Golden CONTRIBUTORS * Karen Etheridge * Matt S Trout * Olivier Mengué * Toby Inkster 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