KeyPathEditable Complete Source code including consumption

ModifyStructPropertyUsingKeyPath.swift

enum KeyPathError: Error {
    case unableToCast(String)
}

protocol KeyPathEditable {
    func update<KeyPathType>(path: PartialKeyPath<Self>, to value: KeyPathType) throws -> Self
}

extension KeyPathEditable {
    func update<KeyPathType>(path: PartialKeyPath<Self>, to value: KeyPathType) throws -> Self {
        guard let writableKeyPath = path as? WritableKeyPath<Self, KeyPathType> else {
            throw KeyPathError.unableToCast("because of passed \(value) value data type")
        }
        var copy = self
        copy[keyPath: writableKeyPath] = value
        return copy
    }
}

struct User: KeyPathEditable {
    typealias Root = User
    private(set) var name: String
    private(set) var age: Int
    private(set) var property: Property
}

struct Property: KeyPathEditable {
    private(set) var areaName: String
    private(set) var size: String
    private(set) var name: String
}

let property = Property(areaName: "Sector 14", size: "2400 sq ft", name: "Mark villa")
let updatedProperty = try? property.update(path: \Property.areaName, to: "Bangalore")
print(updatedProperty?.areaName ?? property.areaName)

let user = User(name: "Me", age: 16, property: Property(areaName: "Sector 14", size: "2400 sq ft", name: "Mark villa"))

do {
    let latestData = try user.update(path: \User.property, to: Property(areaName: "Sector 4", size: "1200 sq ft", name: "Mark villa"))
    print(latestData.property)
} catch let error {
    print(error)
}

let latestUserData = try? user.update(path: \User.property.name, to: "Euphoria")
print(latestUserData?.property.name ?? user.property.name)