I also use can() to take references to methods. Such as in:

if ($whatever) {
  $self->{callback} = $self->can('a');
} else {
  $self->{callback} = sub {1};
}
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Or to use optimization if possible:

open F, '>', $self->{filename};
if ($other->can('fetch')) {
  print F, $other->fetch();
} else {
  while (my $line = $other->read()) {
    print F, $line;
  }
}
close F;
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