9.12 Faster Getters and Setters

Because you're going to play nice and always call the getters and setters instead of reaching into the data structure, getters and setters are called frequently. To save a teeny-tiny bit of time, you might see these getters and setters written as:

## in Animal
sub color {
sub set_color {
  $_[0]->{Color} = $_[1];

Here's an alternate way to access the arguments: $_[0] is used in place, rather than with a shift. Functionally, this example is identical to the previous implementation, but it's slightly faster, at the expense of some ugliness.