What makes Swift's "Optional" safer than Objective-C's "nil"?

Question

Apple seems to claim that the Optional type in Swift is safer than nil in Objective-C, but I don't understand why this is so.

What are the salient differences in implementation that make Optionals safer than nil, and how will this affect my code?

Answer 1

In general, in programming we want to avoid variables that have no value (null or nil) because using them often results in undefined behaviour (exceptions, errors, crashes).

For example, it is a common practice for Array references to be set to empty arrays instead of nil. On an empty array we can use all the Array methods, e.g. indexOf or count. Using them on nil would result in a crash.

Optionals allow us to specify that some variables are never empty, therefore we can use them safely and the compiler checks that nil is never assigned to them. Also, the compiler enforces that every conversion from optionals to non-optionals is explicit (we are always checking for nil when needed).

So the answer would be that optionals:

1. Enforce good programming practices.
2. Allow for better code checking at compilation time

Thus preventing programming errors.

Also note that the you should always try to avoid optionals when possible. The greatest power of optionals is the fact that most variables are not optionals.