Class::Accessor - phpMan

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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".

  Moose-like
    By popular demand we now have a simple Moose-like interface. You can now
    do:

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

    Currently only the "is" attribute is supported.

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.

  new
        my $obj = Foo->new;
        my $obj = $other_obj->new;

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

    It takes an optional %fields hash which is used to initialize the object
    (handy if you use read-only accessors). The fields of the hash
    correspond to the names of your accessors, so...

        package Foo;
        use base qw(Class::Accessor);
        Foo->mk_accessors('foo');

        my $obj = Foo->new({ foo => 42 });
        print $obj->foo;    # 42

    however %fields can contain anything, new() will shove them all into
    your object.

MAKING ACCESSORS
  follow_best_practice
    In Damian's Perl Best Practices book he recommends separate get and set
    methods with the prefix set_ and get_ to make it explicit what you
    intend to do. If you want to create those accessor methods instead of
    the default ones, call:

        __PACKAGE__->follow_best_practice

    before you call any of the accessor-making methods.

  accessor_name_for / mutator_name_for
    You may have your own crazy ideas for the names of the accessors, so you
    can make those happen by overriding "accessor_name_for" and
    "mutator_name_for" in your subclass. (I copied that idea from
    Class::DBI.)

  mk_accessors
        __PACKAGE__->mk_accessors(@fields);

    This creates accessor/mutator methods for each named field given in
    @fields. Foreach field in @fields it will generate two accessors. One
    called "field()" and the other called "_field_accessor()". For example:

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

    See "Overriding autogenerated accessors" in CAVEATS AND TRICKS for
    details.

  mk_ro_accessors
      __PACKAGE__->mk_ro_accessors(@read_only_fields);

    Same as mk_accessors() except it will generate read-only accessors (ie.
    true accessors). If you attempt to set a value with these accessors it
    will throw an exception. It only uses get() and not set().

        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.

  mk_wo_accessors
      __PACKAGE__->mk_wo_accessors(@write_only_fields);

    Same as mk_accessors() except it will generate write-only accessors (ie.
    mutators). If you attempt to read a value with these accessors it will
    throw an exception. It only uses set() and not get().

    NOTE I'm not entirely sure why this is useful, but I'm sure someone will
    need it. If you've found a use, let me know. Right now it's here for
    orthogonality and because it's easy to implement.

        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.

  Modifying the behavior of the accessor
    Rather than actually modifying the accessor itself, it is much more
    sensible to simply override the two key methods which the accessor
    calls. Namely set() and get().

    If you -really- want to, you can override make_accessor().

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

    set() defines how generally one stores data in the object.

    override this method to change how data is stored by your accessors.

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

    get() defines how data is retrieved from your objects.

    override this method to change how it is retrieved.

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

    Generates a subroutine reference which acts as an accessor for the given
    $field. It calls get() and set().

    If you wish to change the behavior of your accessors, try overriding
    get() and set() before you start mucking with make_accessor().

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

    Generates a subroutine reference which acts as a read-only accessor for
    the given $field. It only calls get().

    Override get() to change the behavior of your accessors.

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

    Generates a subroutine reference which acts as a write-only accessor
    (mutator) for the given $field. It only calls set().

    Override set() to change the behavior of your accessors.

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.

  Don't make a field called DESTROY
    This is bad. Since DESTROY is a magical method it would be bad for us to
    define an accessor using that name. Class::Accessor will carp if you try
    to use it with a field named "DESTROY".

  Overriding autogenerated accessors
    You may want to override the autogenerated accessor with your own, yet
    have your custom accessor call the default one. For instance, maybe you
    want to have an accessor which checks its input. Normally, one would
    expect this to work:

        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(@_);
        }

    There's a subtle problem in the last example, and it's in this line:

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

    If we look at how Foo was defined, it called mk_accessors() which stuck
    email() right into Foo's namespace. There *is* no SUPER::email() to
    delegate to! Two ways around this... first is to make a "pure" base
    class for Foo. This pure class will generate the accessors and provide
    the necessary super class for Foo to use:

        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);

    And now Foo::email() can override the generated
    Pure::Organic::Foo::email() and use it as SUPER::email().

    This is probably the most obvious solution to everyone but me. Instead,
    what first made sense to me was for mk_accessors() to define an alias of
    email(), _email_accessor(). Using this solution, Foo::email() would be
    written with:

        return $self->_email_accessor(@_);

    instead of the expected SUPER::email().

AUTHORS
    Copyright 2017 Marty Pauley <marty+perl AT 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.

  ORIGINAL AUTHOR
    Michael G Schwern <schwern AT pobox.com>

  THANKS
    Liz and RUZ for performance tweaks.

    Tels, for his big feature request/bug report.

    Various presenters at YAPC::Asia 2009 for criticising the non-Moose
    interface.

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.