A type-safe String identifier for objects

Identifier.swift

/// Useful as a type-safe String identifier for objects, records, etc.
/// Generic type A is the type of the object being "identified".
public struct Identifier<A>: Equatable, Hashable, Comparable {
  public let string: String

  public init(_ string: String) {
    self.string = string
  }

  public var hashValue: Int {
    return debugDescription.hashValue
  }

  public static func ==<A>(lhs: Identifier<A>, rhs: Identifier<A>) -> Bool {
    return lhs.string == rhs.string
  }

  public static func < <A>(lhs: Identifier<A>, rhs: Identifier<A>) -> Bool {
    return lhs.string < rhs.string
  }
}

extension Identifier: ExpressibleByStringLiteral {
  public init(stringLiteral value: String) {
    self.string = value
  }
}

extension Identifier: CustomStringConvertible {
  public var description: String {
    return string
  }
}

extension Identifier: CustomDebugStringConvertible {
  public var debugDescription: String {
    return "\(Identifier.self)(\(string))"
  }
}

extension Identifier: CustomPlaygroundQuickLookable {
  public var customPlaygroundQuickLook: PlaygroundQuickLook {
    return PlaygroundQuickLook.text(string)
  }
}

main.swift

protocol Record {
  associatedtype ID = Identifier<Self>
  var id: ID { get }
}

struct Order: Record {
  let id: ID
}

let order = Order(id: "123")

Compatible with Swift 3.0 and higher