Swift Tutorial - Tutorialspoint

Before a class instance needs to be deallocated 'deinitializer' has to be called to deallocate
the memory space. The keyword 'deinit' is used to deallocate the memory spaces occupied
by the system resources. Deinitialization is available only on class types.

Deinitialization to Deallocate Memory Space

Swift automatically deallocates your instances when they are no longer needed, to free up
resources. Swift handles the memory management of instances through automatic
reference counting (ARC), as described in Automatic Reference Counting. Typically you
don't need to perform manual clean-up when your instances are deallocated. However,
when you are working with your own resources, you might need to perform some
additional clean-up yourself. For example, if you create a custom class to open a file and
write some data to it, you might need to close the file before the class instance is
deallocated.

var counter = 0 ; // for reference counting

class baseclass {

init() {

counter++;

}

deinit {

counter--;

}

}

var print: baseclass? = baseclass()

println(counter)

print = nil

println(counter)

When we run the above program using playground, we get the following result:

1

0

When print = nil statement is omitted the values of the counter retains the same since it
is not deinitialized.

var counter = 0 ; // for reference counting

26. SWIFT – DEINITIALIZATION.............................................................................................