mapfilter playground

import Foundation

var strings = ["one", "two", "three", "four"]

extension Array {

    func mapFilter<U>(transform: (T) -> U?) -> [U] {
        var o = [U]()
        
        for e in self {
            if let p = transform(e) {
                o.append(p)
            }
        }
        
        return o
    }

}


let n:[Int] = strings.mapFilter {
    if countElements($0) < 4 {
        return 1
    }
    return nil
}


n