ch16.041_best

Perl Best Practices the source code

##############################################################################
##   Code fragment (Recommended) from Chapter 16 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;



BEGIN {

Readonly my $COMMA => q{,};

package Coerced;
use Class::Std;
{
    my %elements_of : ATTR( init_arg => 'elem' );

    sub count {
        my ($self) = @_;
        return scalar @{ $elements_of{ident $self} }; 
    }
    
    sub as_str {
        my ($self) = @_;
        return sprintf '(%s)', join $COMMA, @{ $elements_of{ident $self} }; 
    }
    
    sub is_okay {
        my ($self) = @_;
        return !$self->Houston_We_Have_A_Problem();
    }
    
    use overload (
        q{0+}   => 'count',
        q{""}   => 'as_str',
        q{bool} => 'is_okay',

        fallback => 1,
    );

    sub Houston_We_Have_A_Problem {
        return 1;
    }
}

}

my $coercable = Coerced->new({elem => [10..17]});

print "str: '$coercable'\n";
print "num: ", 0+$coercable, "\n";
if (!$coercable) {
    print "We have a problem (as expected)\n"
}