Generic Swift Dictionary Extension for nil filtering

Question

I\'m looking for a type safe, generic version of this answer.

This is the method signature I\'m looking for:

extension Dictionary where Value == Opti         


        

Answer 1

Update: As of Swift 5 this would be:

let filtered = dict.compactMapValues { $0 }

Update: As of Swift 4, you can simply do

let filtered = dict.filter( { $0.value != nil }).mapValues( { $0! })

It is currently being discussed if Dictionary should get a compactMapValues method which combines filter and mapValues.

---

(Previous answer:) You can use the same "trick" as in How can I write a function that will unwrap a generic property in swift assuming it is an optional type? and Creating an extension to filter nils from an Array in Swift: define a protocol to which all optionals conform:

protocol OptionalType {
    associatedtype Wrapped
    func intoOptional() -> Wrapped?
}

extension Optional : OptionalType {
    func intoOptional() -> Wrapped? {
        return self
    }
}

Then your dictionary extension can be defined as:

extension Dictionary where Value: OptionalType {
    func filterNil() -> [Key: Value.Wrapped] {
        var result: [Key: Value.Wrapped] = [:]
        for (key, value) in self {
            if let unwrappedValue = value.intoOptional() {
                result[key] = unwrappedValue
            }
        }
        return result
    }
}

Example:

let dict = ["mail": nil, "name": "John Doe"] // Type is [String : String?]
let filtered = dict.filterNil() // Type is [String : String]
print(filtered) // Output: ["name": "John Doe"]