NAME

  Class::Accessor - Automated accessor generation

SYNOPSIS

  package Foo;
  use base qw(Class::Accessor);
  Foo->follow_best_practice;
  Foo->mk_accessors(qw(name role salary));
  # or if you prefer a Moose-like interface...
  package Foo;
  use Class::Accessor "antlers";
  has name => ( is => "rw", isa => "Str" );
  has role => ( is => "rw", isa => "Str" );
  has salary => ( is => "rw", isa => "Num" );
  # Meanwhile, in a nearby piece of code!
  # Class::Accessor provides new().
  my $mp = Foo->new({ name => "Marty", role => "JAPH" });
  my $job = $mp->role;  # gets $mp->{role}
  $mp->salary(400000);  # sets $mp->{salary} = 400000 # I wish
  # like my @info = @{$mp}{qw(name role)}
  my @info = $mp->get(qw(name role));
  # $mp->{salary} = 400000
  $mp->set('salary', 400000);

DESCRIPTION

This module automagically generates accessors/mutators for your class.

Most of the time, writing accessors is an exercise in cutting and pasting. You usually wind up with a series of methods like this:

    sub name {
        my $self = shift;
        if(@_) {
            $self->{name} = $_[0];
        }
        return $self->{name};
    }
    sub salary {
        my $self = shift;
        if(@_) {
            $self->{salary} = $_[0];
        }
        return $self->{salary};
    }
  # etc...

One for each piece of data in your object. While some will be unique, doing value checks and special storage tricks, most will simply be exercises in repetition. Not only is it Bad Style to have a bunch of repetitious code, but it's also simply not lazy, which is the real tragedy.

If you make your module a subclass of Class::Accessor and declare your accessor fields with mk_accessors() then you'll find yourself with a set of automatically generated accessors which can even be customized!

The basic set up is very simple:

    package Foo;
    use base qw(Class::Accessor);
    Foo->mk_accessors( qw(far bar car) );

Done. Foo now has simple far(), bar() and car() accessors defined.

Alternatively, if you want to follow Damian's best practice guidelines you can use:

    package Foo;
    use base qw(Class::Accessor);
    Foo->follow_best_practice;
    Foo->mk_accessors( qw(far bar car) );

Note: you must call "follow_best_practice" before calling "mk_accessors".

    package Foo;
    use Class::Accessor "antlers";
    has far => ( is => "rw" );
    has bar => ( is => "rw" );
    has car => ( is => "rw" );

CONSTRUCTOR

Class::Accessor provides a basic constructor, "new". It generates a hash-based object and can be called as either a class method or an object method.

    my $obj = Foo->new;
    my $obj = $other_obj->new;
    my $obj = Foo->new(\%fields);
    my $obj = $other_obj->new(\%fields);

    package Foo;
    use base qw(Class::Accessor);
    Foo->mk_accessors('foo');
    my $obj = Foo->new({ foo => 42 });
    print $obj->foo;    # 42

MAKING ACCESSORS

    __PACKAGE__->follow_best_practice

    __PACKAGE__->mk_accessors(@fields);

    # Generates foo(), _foo_accessor(), bar() and _bar_accessor().
    __PACKAGE__->mk_accessors(qw(foo bar));

  __PACKAGE__->mk_ro_accessors(@read_only_fields);

    package Foo;
    use base qw(Class::Accessor);
    Foo->mk_ro_accessors(qw(foo bar));
    # Let's assume we have an object $foo of class Foo...
    print $foo->foo;  # ok, prints whatever the value of $foo->{foo} is
    $foo->foo(42);    # BOOM!  Naughty you.

  __PACKAGE__->mk_wo_accessors(@write_only_fields);

    package Foo;
    use base qw(Class::Accessor);
    Foo->mk_wo_accessors(qw(foo bar));
    # Let's assume we have an object $foo of class Foo...
    $foo->foo(42);      # OK.  Sets $self->{foo} = 42
    print $foo->foo;    # BOOM!  Can't read from this accessor.

Moose!

If you prefer a Moose-like interface to create accessors, you can use "has" by importing this module like this:

  use Class::Accessor "antlers";

or

  use Class::Accessor "moose-like";

Then you can declare accessors like this:

  has alpha => ( is => "rw", isa => "Str" );
  has beta  => ( is => "ro", isa => "Str" );
  has gamma => ( is => "wo", isa => "Str" );

Currently only the "is" attribute is supported. And our "is" also supports the "wo" value to make a write-only accessor.

If you are using the Moose-like interface then you should use the "extends" rather than tweaking your @ISA directly. Basically, replace

  @ISA = qw/Foo Bar/;

with

  extends(qw/Foo Bar/);

DETAILS

An accessor generated by Class::Accessor looks something like this:

    # Your foo may vary.
    sub foo {
        my($self) = shift;
        if(@_) {    # set
            return $self->set('foo', @_);
        }
        else {
            return $self->get('foo');
        }
    }

Very simple. All it does is determine if you're wanting to set a value or get a value and calls the appropriate method. Class::Accessor provides default get() and set() methods which your class can override. They're detailed later.

    $obj->set($key, $value);
    $obj->set($key, @values);

    $value  = $obj->get($key);
    @values = $obj->get(@keys);

    $accessor = __PACKAGE__->make_accessor($field);

    $read_only_accessor = __PACKAGE__->make_ro_accessor($field);

    $write_only_accessor = __PACKAGE__->make_wo_accessor($field);

EXCEPTIONS

If something goes wrong Class::Accessor will warn or die by calling Carp::carp or Carp::croak. If you don't like this you can override _carp() and _croak() in your subclass and do whatever else you want.

EFFICIENCY

Class::Accessor does not employ an autoloader, thus it is much faster than you'd think. Its generated methods incur no special penalty over ones you'd write yourself.

  accessors:
              Rate  Basic   Fast Faster Direct
  Basic   367589/s     --   -51%   -55%   -89%
  Fast    747964/s   103%     --    -9%   -77%
  Faster  819199/s   123%    10%     --   -75%
  Direct 3245887/s   783%   334%   296%     --
  mutators:
              Rate    Acc   Fast Faster Direct
  Acc     265564/s     --   -54%   -63%   -91%
  Fast    573439/s   116%     --   -21%   -80%
  Faster  724710/s   173%    26%     --   -75%
  Direct 2860979/s   977%   399%   295%     --

Class::Accessor::Fast is faster than methods written by an average programmer (where "average" is based on Schwern's example code).

Class::Accessor is slower than average, but more flexible.

Class::Accessor::Faster is even faster than Class::Accessor::Fast. It uses an array internally, not a hash. This could be a good or bad feature depending on your point of view.

Direct hash access is, of course, much faster than all of these, but it provides no encapsulation.

Of course, it's not as simple as saying "Class::Accessor is slower than average". These are benchmarks for a simple accessor. If your accessors do any sort of complicated work (such as talking to a database or writing to a file) the time spent doing that work will quickly swamp the time spend just calling the accessor. In that case, Class::Accessor and the ones you write will be roughly the same speed.

EXAMPLES

Here's an example of generating an accessor for every public field of your class.

    package Altoids;
    use base qw(Class::Accessor Class::Fields);
    use fields qw(curiously strong mints);
    Altoids->mk_accessors( Altoids->show_fields('Public') );
    sub new {
        my $proto = shift;
        my $class = ref $proto || $proto;
        return fields::new($class);
    }
    my Altoids $tin = Altoids->new;
    $tin->curiously('Curiouser and curiouser');
    print $tin->{curiously};    # prints 'Curiouser and curiouser'
    # Subclassing works, too.
    package Mint::Snuff;
    use base qw(Altoids);
    my Mint::Snuff $pouch = Mint::Snuff->new;
    $pouch->strong('Blow your head off!');
    print $pouch->{strong};     # prints 'Blow your head off!'

Here's a simple example of altering the behavior of your accessors.

    package Foo;
    use base qw(Class::Accessor);
    Foo->mk_accessors(qw(this that up down));
    sub get {
        my $self = shift;
        # Note every time someone gets some data.
        print STDERR "Getting @_\n";
        $self->SUPER::get(@_);
    }
    sub set {
        my ($self, $key) = splice(@_, 0, 2);
        # Note every time someone sets some data.
        print STDERR "Setting $key to @_\n";
        $self->SUPER::set($key, @_);
    }

CAVEATS AND TRICKS

Class::Accessor has to do some internal wackiness to get its job done quickly and efficiently. Because of this, there's a few tricks and traps one must know about.

Hey, nothing's perfect.

    package Foo;
    use base qw(Class::Accessor);
    Foo->mk_accessors(qw(email this that whatever));
    # Only accept addresses which look valid.
    sub email {
        my($self) = shift;
        my($email) = @_;
        if( @_ ) {  # Setting
            require Email::Valid;
            unless( Email::Valid->address($email) ) {
                carp("$email doesn't look like a valid address.");
                return;
            }
        }
        return $self->SUPER::email(@_);
    }

    return $self->SUPER::email(@_);

    package Pure::Organic::Foo;
    use base qw(Class::Accessor);
    Pure::Organic::Foo->mk_accessors(qw(email this that whatever));
    package Foo;
    use base qw(Pure::Organic::Foo);

    return $self->_email_accessor(@_);

AUTHORS

Copyright 2017 Marty Pauley <marty+perl@martian.org>

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. That means either (a) the GNU General Public License or (b) the Artistic License.

SEE ALSO

See Class::Accessor::Fast and Class::Accessor::Faster if speed is more important than flexibility.

These are some modules which do similar things in different ways Class::Struct, Class::Methodmaker, Class::Generate, Class::Class, Class::Contract, Moose, Mouse

See Class::DBI for an example of this module in use.