Creating an extension to filter nils from an Array in Swift

Question

I\'m trying to write an extension to Array which will allow an array of optional T\'s to be transformed into an array of non-optional T\'s.

e.g. this could be writte

Answer 1

Since Swift 2.0 it is possible to add a method that works for a subset of types by using where clauses. As discussed in this Apple Forum Thread this can be used to filter out nil values of an array. Credits go to @nnnnnnnn and @SteveMcQwark.

As where clauses do not yet support generics (like Optional), a workaround is necessary via a Protocol.

protocol OptionalType {  
    typealias T  
    func intoOptional() -> T?  
}  

extension Optional : OptionalType {  
    func intoOptional() -> T? {  
        return self.flatMap {$0}  
    }  
}  

extension SequenceType where Generator.Element: OptionalType {  
    func flatten() -> [Generator.Element.T] {  
        return self.map { $0.intoOptional() }  
            .filter { $0 != nil }  
            .map { $0! }  
    }  
}  

let mixed: [AnyObject?] = [1, "", nil, 3, nil, 4]  
let nonnils = mixed.flatten()    // 1, "", 3, 4