Does Swift have a null coalescing operator and if not, what is an example of a custom operator?

Question

A common feature in many languages, the Null Coalescing Operator, is a binary operator often used to shorten expressions of the type:

x = possiblyNullValue NCO valueIfNull 

…where NCO is a placeholder for the language’s null coalescing operator.

Objective C's Null Coalescing Operator is ?:, so the expression would be:

x = possiblyNullValue ?: valueIfNull 

The above expression is also equivalent to the use of tertiary operator:

 x =  someTestForNotNull( possiblyNullValue ) ? possiblyNullValue : valueIfNull 

Advantages of a Null Coalescing Operator

• More readable code (especially with long, descriptive variable names)
• Reduced possibility of typographic errors (tested var is typed only once)
• No double evaluation of the tested variable where the tested variable is a getter, since its accessed once (or the need to cache it to intentionally avoid double evaluation).

Answer 1

As of Swift 2.2 (Xcode 6, beta 5) it's ??

var x: Int? var y: Int? = 8  var z: Int = x ?? 9000 // z == 9000  z = y ?? 9001 // z == 8 

a ?? b is equivalent to the following code:

a != nil ? a! : b 

And as of Beta 6, you can do this:

x ?? y ?? 1 == 8