NAME
Class::Accessor::Constructor - Constructor generator
VERSION
version 1.111590
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 Sub::Documentation.
METHODS
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 munged beforehand - 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 == 2
Defaults 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 munged beforehand 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 doing a tie() on
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.
INSTALLATION
See perlmodinstall for information and options on installing Perl
modules.
BUGS AND LIMITATIONS
No bugs have been reported.
Please report any bugs or feature requests through the web interface at
<http://rt.cpan.org/Public/Dist/Display.html?Name=Class-Accessor-Constru
ctor>.
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://search.cpan.org/dist/Class-Accessor-Constructor/>.
The development version lives at
<http://github.com/hanekomu/Class-Accessor-Constructor> and may be
cloned from <git://github.com/hanekomu/Class-Accessor-Constructor.git>.
Instead of sending patches, please fork this project using the standard
git and github infrastructure.
AUTHOR
Marcel Gruenauer <marcel@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2007 by Marcel Gruenauer.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.