package Gadget;

#
# 'build' new gadget...
# return undef on fail.
#
sub new {
  my ($proto, $name, %args) = @_;
  my $self = bless {}, $proto;
   
  $self->{name} = $name;

  . . . work with %args . . .

  return $self;
}

#
# check if a gadget has already been built.
#
sub is_built {
  my ($self, $name) = @_;

  return exists %_built_gadgets{$name};
}
1;

package main;

my $g1 = new Gadget('knob');

. . . create a bunch of other gadgets . . .

if ($g1->is_built($athing_name)) {
  print "Gadget '$athing_name' has already been built!!\n";
} else {
  . . . do something useful here . . .
}