Property wrapper that allows for properties to be encoded as references by ID and resolved while decoding.

CodableReference.swift

protocol ReferenceEncodable: Identifiable {
    static var referenceStorageKey: CodingUserInfoKey { get }
}

extension ReferenceEncodable {
    static var referenceStorageKey: CodingUserInfoKey {
        CodingUserInfoKey(rawValue: String(describing: Self.self) + "ReferenceStorage")!
    }
}

@propertyWrapper
struct CodableReference<T>: Hashable where T: ReferenceEncodable, T.ID: Codable & Hashable {
    var wrappedValue: T
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(wrappedValue.id)
    }
    
    static func ==(lhs: Self, rhs: Self) -> Bool {
        lhs.wrappedValue.id == rhs.wrappedValue.id
    }
}

extension CodableReference: Codable {
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(wrappedValue.id)
    }
    
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let id = try container.decode(T.ID.self) 
        
        guard let storage = decoder.userInfo[T.referenceStorageKey] as? [T] else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Couldn't find reference storage for type \(String(describing: T.self)), decoder is missing a userInfo key \(T.referenceStorageKey.rawValue) of type [\(String(describing: T.self))]")
        }
        
        guard let concreteValue = storage.first(where: { $0.id == id }) else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Couldn't find \(String(describing: T.self)) with id \(id)")
        }
        
        self.init(wrappedValue: concreteValue)
    }
}

Context: https://rambo.codes/posts/2022-01-04-encoding-and-decoding-references-to-other-types-with-codable