Using pattern matching with ternary if operator

Question

Is it possible to use pattern matching with ternary if operator?

Consider the following examples:

let someString: String? = ...

if let embedURL = embedURL {
    return NSURL(string: embedURL)
} else {
    return nil
}

This is verbose. I would like to be able to do something like this:

return let someString = someString ? NSURL(string: someString) : nil

or

return case let .Some(someString) = someString ? NSURL(string: someString) : nil

But the compiler does not accept that. I know that I could add an initializer to NSURL which accepts optional string, use normal if statement or even switch statement, but I would like to know if it is possible to do with the ternary if operator, or whether it will be possible at some point in the future.

Answer 1

You cannot use pattern matching in the condition of the ternary conditional operator. But you can use the flatMap() method of optionals instead:

/// Returns `nil` if `self` is nil, `f(self!)` otherwise.
public func flatMap<U>(@noescape f: (Wrapped) throws -> U?) rethrows -> U?

In your case:

let someString: String? = ...
let url = someString.flatMap { NSURL(string: $0) }

The type of the expression is NSURL?, and it evaluates to nil if someString == nil or if NSURL(string:) returned nil.

As @Cosyn noticed, the last line can also be written as

let url = someString.flatMap(NSURL.init)

Answer 2

You don't need to use pattern matching to achieve this.

return someString != nil ? NSURL(string: someString!) : nil

Is as close as you can get using the ternary operator as far as I can tell.