There are various ways. The least dirty is to use the AUTOLOAD system as in the following.

package Foo;

use strict;
use vars qw($AUTOLOAD);
use Carp qw(croak);

sub new { bless {}, __PACKAGE__ }

sub add_method {
    my ($self, $name, $code) = @_;

    ### This following chunk could use Scalar::Util::blessed
    ### if they have perl 5.8 installed.  We will operate without it
    if (! ref $code) {
        # scary and sort of ugly but thats what the OP wanted
        $code = eval $code;
    }

    # (! Scalar::Util::reftype($code) ne 'CODE') {
    if (! UNIVERSAL::isa($code, 'CODE')) {
        croak "Usage : add_method(method => sub {})\n
                       add_method(method => 'sub {}')";
    }

    $self->{'_methods'}->{$name} = $code;
}

sub AUTOLOAD {
    my $self = shift;
    my $name = $AUTOLOAD =~ /(\w+)$/ ? $1 : croak "Invalid method \"$A
+UTOLOAD\"";

    my $code = $self->{'_methods'}->{$name}
        || croak "No such method \"$name\" via package ".__PACKAGE__;

    $self->$code(@_);
}

my $foo = Foo->new;
$foo->add_method(bar => sub { print "bar\n" });
$foo->add_method(baz => 'sub { print "baz\n" }');

$foo->bar;
$foo->baz;
[download]

The other way of doing this sort of thing involves manipulating the symbol table which isn't hard, but I wouldn't recommend if you are just starting out.

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