The following lines create an instance of the Circle class named circle within the scope of a generatedCircleRadius function. The code within the function uses the created instance to access and return the value of its radius property. In this case, the code uses the let keyword to declare an immutable reference to the Circle instance named circle. An immutable reference is also known as a constant reference because we cannot replace the reference held by the circle constant to another instance of Circle. When we use the var keyword, we declare a reference that we can change later.
After we define the new function, we will call it. Note that the screenshot displays the results of the execution of the initializer and then the deinitializer. Swift destroys the instance after the circle constant goes out of scope because its reference count goes down from one to zero; therefore, there is no reason to keep the instance alive. Enter the following lines in the...