Open Radar

 
Summary:
Swift could use an operator that takes a T? on the left side and a T on the right, and turns the right side if the left side is nil.

In other words, it needs something like:

func ?: <T> (lhs: T?, rhs: @auto_closure Void -> T) -> T {
    return lhs ? lhs : rhs()
}

Steps to Reproduce:

1. Create an optional chain, e.g.:

    john?.residence?.address

2. Try to elegantly specify a default for that chain (in this case, a default mailing address).

Expected Results:
There is some way to do this in a single expression without re-evaluating the optional chain.

Actual Results:
You can either evaluate the optional chain twice:

    john?.residence?.address ? john?.residence?.address : defaultAddress

Or you can use a heavier construct:

    var optionalAddress = john?.residence?.address
    if !optionalAddress { optionalAddress = defaultAddress }
    let address = optionalAddress!

Notes:
“?:” is the equivalent operator in Objective-C, but I don’t think it feels right for Swift; I don’t imagine this as a boolean operation, but rather as a nil-or-not-nil operation. Perl 6 used “//” for this operation—and in fact, I backported this feature to Perl 5 about a decade ago—but that would clash with comments in Swift. My best suggestion is “??”, which clearly communicates that it’s optional-related, but that syntax is ugly enough that I’m not terribly attached to it.