my $method = $this->{ACTIVITIES}->{$this->{ACT}}->{'func'};
$this->$method($arg);

##</code><code>##

$this->{ACTIVITIES} = {
    Sale => {},
    ....
};

##</code><code>##

$this->{ACTIVITIES} = {
	Sale => {
		func      => 'total_sold',
		datefield => 'date_sold',
	},
	Purchase => {
		func      => 'total_bought',
		datefield => 'date_bought',
	},
};