# If velocity is defined, use it, otherwise don't.
# Note that just the concatenation arg is guarded,
# so you still get an error if $b is not a hashref.

$a = $b->{'velocity'}^^ . ' mph' // 'unknown';

# Safe dereferencing of $d (it may be undefined).
# Note that the second dereference is normal,
# so parent() returning undef would trigger an error.

$c = $d^^ ->  parent  ->  name;

# Safe dereferencing of $d (it may be undefined).
# Note that the second dereference is normal,
# so a nonexistent 'parent' component would be created.

$c = $d^^ ->{'parent'}->{'name'};