#!/usr/local/bin/perl -w
# Doable.pm
# my dbc OOPerl "interface"

use strict;
use warnings;
use FindBin::libs;
use Class::Contract;

package Doable; {
    unless( eval {
        contract {
            # constant
            class attr 'NADA';
            invar { ${self->NADA} = 0; };

            abstract ctor 'new';
            abstract dtor;

            # Control
            abstract method 'doTheThing';

            # Test: DON'T implement doThatThing
            # and hope an exception is raised.
            abstract method 'doThatThing';
                pre { defined ${Doable::caller} };
        }; # end contract

        sub new;
        sub DESTROY;
        sub doTheThing;
        # sub doThatThing;

    1; } # end eval

    ) { die( "\n\nThere has been a breach of contract.\n\n" ); } # end unless

} 1; # end Doable

##</code><code>##

#!/usr/local/bin/perl -w
# Doer.pm
# my OOPerl "implementation"

use strict;
use warnings;
use FindBin::libs;
use Class::Contract;
use private qw(_semprini);
use protected qw(_friendly);
use public qw(face);

# Should be implementing rather than overloading or overriding
use overload "Doable::doTheThing" => "Doer::doTheThing";

use Doable;

# I want to IMPLEMENT, 
# not INHERIT, but anyway...
package Doer; @Doer::ISA = qw(Doable); {
    sub new {
        my $classname = shift;
        my $self = bless { }, $classname;
        $self->{_semprini} = 'naughty';
        $self->{face} = 'blank';
        return($self);
    } # end new

    sub DESTROY {
        my $self = shift;
    } # end DESTROY

    sub doTheThing {
        print"\nTesting...\n\n";
    } # end doTheThing

    # Don't uncomment unless testing.
    # sub doThatThing { return(0); } # end doThatThing

} 1; # end Doer

##</code><code>##

#!/usr/local/bin/perl -w
# MyApp.pl
# my OOPerl "application"

use strict;
use warnings;
use private qw(_MyApp _main _d);
use Doer;

# I don't want to inherit here, 
# I just want to "use" and make sub calls
package _MyApp; @_MyApp::ISA = qw(Doer); {
    sub _main; {
        my $_d = Doer->new;             # constructor
        $_d->doTheThing;                # method
        # print $_d->NADA;              # can't see the constant
        $_d->DESTROY;                   # destructor
        print("\nDone! exiting...\n\n");
        exit(0);
    } # end _main

} 1; # end _MyApp