NAME¶
Class::Std::Utils - Utility subroutines for building "inside-out"
objects
VERSION¶
This document describes Class::Std::Utils version 0.0.3
SYNOPSIS¶
use Class::Std::Utils;
# Constructor for anonymous scalars...
my $new_object = bless anon_scalar(), $class;
# Convert an object reference into a unique ID number...
my $ID_num = ident $new_object;
# Extract class-specific arguments from a hash reference...
my %args = extract_initializers_from($arg_ref);
DESCRIPTION¶
This module provides three utility subroutines that simplify the creation of
"inside-out" classes. See Chapters 15 and 16 of "Perl Best
Practices" (O'Reilly, 2005) for details.
INTERFACE¶
- "anon_scalar()"
- This subroutine is always exported. It takes no arguments
and returns a reference to an anonymous scalar, suitable for blessing as
an object.
- "ident()"
- This subroutine is always exported. It takes one
argument--a reference-- and acts exactly like the
"Scalar::Util::refaddr()", returning a unique integer value
suitable for identifying the referent.
- "extract_initializers_from()"
- This subroutine is always exported. It takes one
argument--a hash reference-- and returns a "flattened" set of
key/value pairs extracted from that hash.
The typical usage is:
my %class_specific_args = extract_initializers_from($args_ref);
The argument hash is flattened as described in Chapter 16 of "Perl Best
Practices":
The subroutine is always called with the
original multi-level argument hash from the constructor. It then looks
up the class's own name (i.e. its "caller"
package) in the argument hash, to see if an initializer with that key
has been defined. Finally,
"extract_initializers_for()" returns the flattened
set of key/value pairs for the class's initializer set, by appending
the class-specific initializer subhash to the end of the original
generic initializer hash. Appending the specific initializers after the
generic ones means that any key in the class- specific set will
override any key in the generic set, thereby ensuring that the most
relevant initializers are always selected, but that generic
initializers are still available where no class-specific value has been
passed in.
In other words, given:
my $arg_ref = {
key_1 => 'generic value 1',
key_2 => 'generic value 2',
'Base::Class' => {
key_1 => 'base value 1'
},
'Der::Class' => {
key_1 => 'der value 1'
key_2 => 'der value 2'
},
};
package Base::Class;
use Class::Std::Utils;
my %base_args = extract_initializers_from($arg_ref);
package Der::Class;
use Class::Std::Utils;
my %der_args = extract_initializers_from($arg_ref);
then %base_args would be initialized to:
(
key_1 => 'base value 1',
key_2 => 'generic value 2',
'Base::Class' => {
key_1 => 'base value 1',
},
'Der::Class' => {
key_1 => 'der value 1',
key_2 => 'der value 2',
},
)
whilst %der_args would be initialized to:
(
key_1 => 'der value 1',
key_2 => 'der value 2',
'Base::Class' => {
key_1 => 'base value 1',
},
'Der::Class' => {
key_1 => 'der value 1',
key_2 => 'der value 2',
},
)
That is, the top-level entries would be replaced by any second-level entries
with the same key that appear in a top-level entry of the same name as the
calling package.
This means that each class can just refer to $args{key_1} and $args{key_2} and
be confident that the resulting values will be the most specific available for
that class.
DIAGNOSTICS¶
- "%s initializer must be a nested hash"
- Thrown by "extract_initializers_from()". You
specified a top-level key that has the same name of the current class, but
the value of that key wasn't a hash reference.
CONFIGURATION AND ENVIRONMENT¶
Class::Std::Utils requires no configuration files or environment variables.
DEPENDENCIES¶
Thsi module requires both the "Scalar::Util" and
"List::Util" modules, which are standard in Perl 5.8 and available
from the CPAN for earlier versions of Perl.
INCOMPATIBILITIES¶
None reported.
SEE ALSO¶
The "Class::Std" module
"Perl Best Practices", O'Reilly, 2005.
BUGS AND LIMITATIONS¶
No bugs have been reported.
Please report any bugs or feature requests to
"bug-class-std-utils@rt.cpan.org", or through the web interface at
<
http://rt.cpan.org>.
AUTHOR¶
Damian Conway "<DCONWAY@cpan.org>"
LICENCE AND COPYRIGHT¶
Copyright (c) 2005, Damian Conway "<DCONWAY@cpan.org>". All
rights reserved.
This module is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.
DISCLAIMER OF WARRANTY¶
BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE
SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE
STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE
SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR
IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO
THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE
PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR
CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY
COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE
SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO
LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR
THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER
SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.