sub new { my $class = shift; my %params = @_; my $self = {}; foreach (qw(param1 param2 param3)) { $self->{$_} = $params{$_} } # further initialization. # ... bless $self, $class; } #### use fields qw(param1 param2 param3); sub new { my ClassName $self = shift; unless (ref $self) { $self = fields::new($self); } # initialization # ... return $self; }