ch17.009_best

Perl Best Practices the source code

##############################################################################
##   Code fragment (Recommended) from Chapter 17 of "Perl Best Practices"   ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;


sub _Class::cannot {
    # What kind of coercion cannot be done?
    my ($coerce) = @_;
 
    # Build a subroutine with the corresponding error message...
    return sub {
        my ($self) = @_;
        croak sprintf qq{Can't $coerce}, ref $self;
    };
}
 
# and later...
 

package Process::Queue;
{
    use overload (
        # Type coercions don't make sense for process queues...
        q{""}   => _Class::cannot('stringify a %s'),
        q{0+}   => _Class::cannot('numerify a %s'),
        q{bool} => _Class::cannot('get the boolean value of a %s'),
    );
}
 
# and later still...
 
package Socket;
{
    use overload (
        # Type coercions don't make sense for sockets...
        q{""}   => _Class::cannot('stringify a %s'),
        q{0+}   => _Class::cannot('numerify a %s'),
        q{bool} => _Class::cannot('get the boolean value of a %s'),
    );
}