Add constraints to generic parameters in extension

Question

I have this function:

func flatten(dict: Dictionary>) -> Dictionary {
    v         


        

Answer 1

You can do it in a simpler way. This works with Swift 4:

extension Dictionary {
    func flatten() -> [Key: Wrapped] where Value == Optional {
         return filter { $1 != nil }.mapValues { $0! }
    }
}

If you don't like the use of higher order functions or need compatibility with previous versions of Swift you can do this as well:

extension Dictionary {
    func flatten() -> [Key: Wrapped] where Value == Optional {
        var result: [Key: Wrapped] = [:]
        for (key, value) in self {
            guard let value = value else { continue }
            result[key] = value
        }
        return result
    }
}