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June 17, 2017 22:15
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//: Playground - noun: a place where people can play | |
import Foundation | |
class DecodableCache<Key,Value> where Key : Hashable { | |
private var values: [Key:Value] = [:] | |
subscript(index: Key) -> Value? { | |
get { | |
return values[index] | |
} | |
set(newValue) { | |
values[index] = newValue | |
} | |
} | |
} | |
extension Decoder { | |
private var personCache: DecodableCache<Int,Person> { | |
var personCacheKey = "personCache" | |
if let cache = objc_getAssociatedObject(self, &personCacheKey) as? DecodableCache<Int,Person> { | |
return cache | |
} | |
else { | |
let cache = DecodableCache<Int,Person>() | |
objc_setAssociatedObject(self, &personCacheKey, cache, .OBJC_ASSOCIATION_RETAIN) | |
return cache | |
} | |
} | |
func nestedPerson(container: KeyedDecodingContainer<Car.CodingKeys>, forKey key: Car.CodingKeys) throws -> Person { | |
let personContainer = try container.nestedContainer(keyedBy: Car.PersonKeys.self, forKey: key) | |
let personId = try personContainer.decode(Int.self, forKey: .identifier) | |
if let cachedPerson = personCache[personId] { | |
return cachedPerson | |
} | |
let decodedPerson = try container.decode(Person.self, forKey: key) | |
personCache[personId] = decodedPerson | |
return decodedPerson | |
} | |
} | |
class Person : Codable { | |
let identifier: Int | |
init(identifier: Int) { | |
self.identifier = identifier | |
} | |
} | |
struct Car : Codable { | |
let owner: Person | |
let driver: Person | |
enum CodingKeys: String, CodingKey { | |
case owner | |
case driver | |
} | |
enum PersonKeys: String, CodingKey { | |
case identifier | |
} | |
public init(owner: Person, driver: Person) { | |
self.owner = owner | |
self.driver = driver | |
} | |
public init(from decoder: Decoder) throws { | |
let myContainer = try decoder.container(keyedBy: Car.CodingKeys.self) | |
self.owner = try decoder.nestedPerson(container: myContainer, forKey: .owner) | |
self.driver = try decoder.nestedPerson(container: myContainer, forKey: .driver) | |
} | |
} | |
let kate = Person(identifier: 200) | |
let car = Car(owner: kate, driver: kate) | |
let data = try JSONEncoder().encode(car) | |
let json = String(data: data, encoding: .utf8)! | |
let car2 = try JSONDecoder().decode(Car.self, from: data) | |
print(Unmanaged.passUnretained(car2.owner).toOpaque().debugDescription) | |
print(Unmanaged.passUnretained(car2.driver).toOpaque().debugDescription) |
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