ch16.040_best

来自「Perl Best Practices the source code」· 040_BEST 代码 · 共 59 行

##############################################################################
##   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' );

    # Call count() method whenever object used as number
    sub count : NUMERIFY {   
        my ($self, $ident) = @_;
        return scalar @{ $elements_of{$ident} }; 
    }
    
    # Call as_str() method whenever object used as string
    sub as_str : STRINGIFY { 
        my ($self, $ident) = @_;
        return sprintf '(%s)', join $COMMA, @{ $elements_of{$ident} }; 
    }
    
    # Call is_okay() method whenever object used as boolean
    sub is_okay : BOOLIFY { 
        my ($self) = @_;
        return !$self->Houston_We_Have_A_Problem();
    }

    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"
}