ios - How to make generics in collection type constraint? -

i have been trying extract non-nil values string array. below. but, senior wants able extract non-nil values other types too.

i read, generics me handling different types. how can use generics use following extension work other types too?

getnonnil must return extracted non-nil values of specific type (i.e. if array [string?] must return [string], returns [int] if [int?])

because have further calculations.

what have tried below:

import foundation // extended collection-type collectiontype constrained having element optional strings extension collectiontype self.generator.element == optional<string>{     func getnonnil() -> [string] {         // filter out nil elements , forcefully unwrap them using map         return self.filter({$0 != nil}).map({$0!})     } }  // usage let x: [string?] = ["er", "err", nil, "errr"]  x.getnonnil().foreach { (str) in     print(str) } 

for getnonnil use

x.flatmap { $0 } // returns ["er", "err", "errr"] [string] 

---

for original question, typically introduce protocol optional type (e.g. via muukii/optionalprotocol package):

protocol optionalprotocol {     associatedtype wrapped     var value: wrapped? { } }  extension optional: optionalprotocol {     public var value: wrapped? { return self } }  extension collectiontype self.generator.element: optionalprotocol {     func getnonnil() -> [self.generator.element.wrapped] {         ...     } }