I am with you on the use of delegation. However, you could take your example one step further and use dependency injection to fully decouple the two classes.

 
  package Bar;

  sub new {
      my ($class, %args) = @_;
      bless \%args, $class;
  }

  sub wonk {
      my $self = shift;
      $self->{_foo}->wonk(@_); # delegation!
  }

  package main;

  use Bar;
  use Foo;
  
  my $bar = Bar->new(_foo => Foo->new());
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Now Bar is fully independent of Foo (coupled only by the implied "interface" which consists of the wonk() method). This also makes testing easier.