How to make generics in collection type constraint?

Question

I have been trying to extract non-nil values from the String array. Like below. But, my senior wants it to be able to extract non-nil values from other type

Answer 1

For getNonNil you could simply use

x.flatMap { $0 }
// returns ["Er", "Err", "errr"] which is [String]

---

For the original question, typically you could introduce a protocol to the Optional type (e.g. via the muukii/OptionalProtocol package):

protocol OptionalProtocol {
    associatedtype Wrapped
    var value: Wrapped? { get }
}

extension Optional: OptionalProtocol {
    public var value: Wrapped? { return self }
}

extension CollectionType where Self.Generator.Element: OptionalProtocol {
    func getNonNil() -> [Self.Generator.Element.Wrapped] {
        ...
    }
}