将可选类型转换为非可选类型

Question

The following code throws a compile error:

import UIKit

class Initable {
    required init() {}
}

class NestedObject:Initable {
    var nestedProp:String? = nil
}

class MyObj {
    var name:String? = nil
    var value:Int? = nil
    var otherVals:[String]? = nil
    var nestedObj:NestedObject? = nil
}

let obj = MyObj()
var nestedObj = obj[keyPath: \MyObj.nestedObj]
if(nestedObj == nil) {
    nestedObj = type(of: obj[keyPath: \MyObj.nestedObj]).init()
}
nestedObj![keyPath: \NestedObject.nestedProp] = "NEST ME BABY!!"
obj[keyPath: \MyObj.nestedObj] = nestedObj!

obj

This is due to the fact that type(of: obj[keyPath: \MyObj.nestedObj]) is NestedObject? , which of course cannot be initialized. I need a way to unwrap the optional typing and get the non-optional typing NestedObject .

Assumptions that have to be maintained.

• I must used optionals as there is a chance for nestedObj to be nil.
• I do not know what the type NestedObject is. It could be any type, but I am assured those types are all Initable .
• I need to be able to set a property of my nestedObject via a keypath.
• If nestedObject is nil, I need to create a new NestedObject and set the value via a keypath.

This is a small part of a larger system, so the above assumptions must be considered. I cannot change those.

Answer 1

You can use your optional Wrapped type to initialize your nested object:

let obj = MyObj()
let nestedObj = type(of: obj[keyPath: \MyObj.nestedObj]).Wrapped()
nestedObj[keyPath: \NestedObject.nestedProp] = "NEST ME BABY!!"

print(nestedObj.nestedProp ?? "")  // "NEST ME BABY!!"

---

If you want the resulting object to be optional as well:

let obj = MyObj()
var nestedObj = obj[keyPath: \MyObj.nestedObj]
if nestedObj == nil {
    nestedObj = type(of: obj[keyPath: \MyObj.nestedObj]).Wrapped()
}
nestedObj?[keyPath: \NestedObject.nestedProp] = "NEST ME BABY!!"

---

You need to add those helpers:

protocol AnyOptional {
    associatedtype Wrapped
    var optional: Optional<Wrapped> { get }
}

extension Optional: AnyOptional {
    var optional: Optional<Wrapped> { self }
}