Thanks. That is exactly what I was looking for. It even works when applying a role during runtime. (This comes quite handy for implementing a dummy backend class which can fake different feature-set. Think something along the line of DBI, where you want to test the DBI class, but not the actual backend like DBD::mysql)

(Moose)

sub BUILD {
  my $self = shift;
  my $mode = $self->get_mode();

  # normally roles are not used/required, but since we manipulate this
  # class' roles at runtime we need to require the role
  if ($mode =~ /R/xmsi) {
    require TLA::Datastore::_readable;
    TLA::Datastore::_readable->meta->apply($self);
  }
  if ($mode =~ /W/xmsi) {
    require TLA::Datastore::_writeable;
    TLA::Datastore::_writeable->meta->apply($self);
  }
  if ($mode =~ /X/xmsi) {
    require TLA::Datastore::_execute;
    TLA::Datastore::_execute->meta->apply($self);
  }
  return;
}
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And later I can test for a specific role:

my $ds = TLA::Datastore::Dummy->new('mode' => 'R');
if ( $ds->DOES('TLA::Datastore::_readable') ) {
  # do stuff
};
[download]