dabrahams

/// Classes whose initializers actually create derived classes
protocol FactoryInitializable {
  /// The type of the least-derived class declared to be FactoryInitializable.
  ///
  /// - Warning: Do not define this in your FactoryInitializable type!
  associatedtype FactoryBase: AnyObject, FactoryInitializable = Self
  // This associatedtype is a trick that captures `Self` at the point where
  // `FactoryInitializable` enters a class hierarchy; in other contexts, `Self`
  // refers to the most-derived type.
}

dabrahams

/// A repository of functionality depending on the conformances of `Model`.
///
/// Conditional conformances provide implementation functions that take a
/// generic argument type with the safe assumption that the argument's concrete
/// type is `Model`.
struct Dispatch<Model> {
  /// Returns `f(a as! Model) as! R1`
  ///
  /// Used by implementation functions to avoid the clutter of casting
  /// explicitly.