NAME
Class::Accessor::Constructor - constructor generator
SYNOPSIS
package MyClass;
use base 'Class::Accessor::Constructor';
__PACKAGE__->mk_constructor;DESCRIPTION
This module generates accessors for your class in the same spirit as Class::Accessor does. While the latter deals with accessors for scalar values, this module provides accessor makers for rather flexible constructors.
The accessor generators also generate documentation ready to be used with Pod::Generated.
ACCESSORS
This section describes the accessor makers offered by this module, and the methods it generates.
mk_constructor
Takes an array of strings as its argument. If no argument is given, it uses new as the default. For each string it creates a class constructor which is quite powerful and flexible. It supports
- customizable munging of arguments
- customizable sorting of arguments
- inherited default values
- an optional init() method
The constructor accepts named arguments - that is, a hash - and will set the hash values on the accessor methods denoted by the keys. For example,
package MyClass;
use base 'Class::Accessor::Constructor';
__PACKAGE__->mk_constructor;
package main;
use MyClass;
my $o = MyClass->new(foo => 12, bar => [ 1..5 ]);is the same as
my $o = MyClass->new;
$o->foo(12);
$o->bar([1..5]);The constructor will also call an init() method, if there is one.
The arguments are pre-munged - if a single argument is a hashref is passed in, it is expanded out, the the key/value pairs - whether originally as a hash ref or a list - may be reordered as typically occurs with perl hashes.
For example:
package Simple;
use base 'Class::Accessor::Constructor';
__PACKAGE__
->mk_constructor
->mk_accessors(qw(a b));
use constant DEFAULTS => (a => 7, b => 'default') ;Somewhere else:
use Simple;
my $test1 = Simple->new; # now a == 7, b == 'default'
my $test2 = Simple->new(a => 1); # now a == 1, b == 'default'
my $test3 = Simple->new(a => 1, b => 2); # now a == 1, b == 2Defaults can be inherited per Data::Inherited's every_hash(). Example:
package A;
use base 'Class::Accessor::Constructor';
__PACKAGE__->mk_constructor->mk_accessors(qw(a b));
use constant DEFAULTS => (a => 7, b => 'default');and
package B;
use base 'A';
use constant DEFAULTS => (a => 23);then
use A;
use B;
my $test1 = A->new; # now a == 7, b == 'default'
my $test2 = B->new; # now a == 23, b == 'default'If a class wants to order some args first, it can define a FIRST_CONSTRUCTOR_ARGS() list, which will be cumulative over inheritance tree due to Data::Inherited. FIRST_CONSTRUCTOR_ARGS() should return a list of argument names that have to come first; if a constructor is called, those arguments are set first, whereas the other ones are set in an unspecified order.
Example:
package Simple;
use base 'Class::Accessor::Constructor';
__PACKAGE__->mk_constructor->mk_accessors(qw(b));
use constant FIRST_CONSTRUCTOR_ARGS => ('b');
# make 'a' dependent on 'b'
sub a {
return $_[0]->{a} if @_ == 1;
$_[0]->{a} = $_[1] + $_[0]->b;
}then
my $test = Simple->new(a => 1, b => 2);will set b first, then set <a> (to 3).
As mentioned, arguments are pre-munged automatically, but you can also customize the munging. By default,
my $test = Simple->new(a => 1, b => 2)is the same as
my $test = Simple->new({ a => 1, b => 2 })Suppose you have a class that has one preferred accessor, and you want to simplify its usage so that if the constructor is called with a single value, it is passed to that preferred accessor.
Given that the Simple class defines
sub MUNGE_CONSTRUCTOR_ARGS {
my $self = shift;
return %{ $_[0] } if @_ == 1 && ref($_[0]) eq 'HASH';
return (b => @_) if @_ % 2; # odd number of args
return @_;
}then an object could be constructed like this
my $test = Simple->new('blah');which would be munged to be equivalent to
my $test = Simple->new(b => 'blah');If you define an init() method, the constructor calls it with the munged args as the very last thing.
mk_constructor_with_dirty
Like mk_constructor(), but also keeps track of whether the object has been modified. This is useful, for example, when you have read the object from a storage and at the end you want to write it back if it has changed. This method generated saves you from having to update a dirty-flag in each accessor. It achieves its purpose by tie-ing the blessed hash that is the object, so there is some performance penalty. But it also works when someone tries to break encapsulation by accessing hash elements directly instead of going via the accessors. See Class::Accessor::Constructor::Base for details.
If you want that behaviour only in a part of your inheritance tree, redefine the constructor at the appropriate point. For example:
package Foo;
use base 'Class::Accessor::Constructor';
__PACKAGE__->mk_constructor;
package Bar;
use base 'Foo';
__PACKAGE__->mk_constructor_with_dirty;Now objects of type Foo will not keep a dirty-flag, but objects of type Bar and its descendants will.
mk_singleton_constructor
Like constructor but constructs a singleton object.
BUGS AND LIMITATIONS
No bugs have been reported.
Please report any bugs or feature requests through the web interface at http://rt.cpan.org.
INSTALLATION
See perlmodinstall for information and options on installing Perl modules.
AVAILABILITY
The latest version of this module is available from the Comprehensive Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find a CPAN site near you. Or see <http://www.perl.com/CPAN/authors/id/M/MA/MARCEL/>.
AUTHORS
Marcel Grünauer, <marcel@cpan.org>
COPYRIGHT AND LICENSE
Copyright 2007-2008 by the authors.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.