Paul Miller

NAME

Object::Previous - find the instance of the object that called your function

SYNOPSIS

    package Human;
    use Object::Previous;

    sub new { bless {hit_points=>(7+int rand 6)} }
    sub hurt_us {
        my $body = shift;
           $body->{hit_points} -= shift;

        if( (int rand 10) == 0 ) {
            # every once in a while, damaging bodies hurts the sword:

            my $sword = previous_object();
               $sword->hurt_us(1+int rand 4);
        }
    }

    package Sword;
    sub new { bless {hit_points=>2} }
    sub hurt_human {
        my $sword = shift;
        my $target = shift;

        $target->hurt_us( 1+int rand 8 );
    }
    sub hurt_us {
        my $sword = shift;
           $sword->{hit_points} -= shift;

        if( $sword->{hit_points} <= 0 ) {
            warn "the attacker's sword broke!";
        }
    }

previous_object

"previous_object" either returns the blessed ref of the caller or undef if it is not possible to find it.

CAVEATS

If you tinker with the @_ in the caller object, "previous_object" won't work. Curiously, certain ways of tinkering don't hurt and others do.

    my $self = shift; # doesn't hurt previous_object()
    shift while @_;   # doesn't hurt previous_object()
    splice @_, 0, 30; # doesn't hurt previous_object()

    unshift @_, "borked"; # breaks previous_object();
    @_ = ();              # breaks previous_object();

Another caveat is that almost everyone thinks this is a really bad idea and/or bad practice.

The only place I've ever seen it actually used in practice is for security in MudOS (LPC, not Perl). LPC has a native previous_object function. It's used to make sure calling objects are really admin-shells or really the mob they're supposed to be -- anywhere you wouldn't want someone to just be able to pass in an appropriate object to subvert the security.

AUTHOR(S)

Most of the code was ripped from Perl and from http://perlmonks.org/, but it was glued together by me.

Paul Miller <jettero@cpan.org>

I am using this software in my own projects... If you find bugs, please please please let me know. :) Actually, let me know if you find it handy at all. Half the fun of releasing this stuff is knowing that people use it.

COPYRIGHT

Copyright (c) 2007-2010 Paul Miller

Licensed under the same terms as Perl itself.

SEE ALSO

perl(1), Devel::Stacktrace, http://perlmonks.org/?node_id=690713, http://perlmonks.org/?node_id=690795, cop.h, pp_ctl.c