[Tips] ViewModel should have equatable with pointer personality.

[muukii]

ViewModel or Store such as having the state and as a reference type, That should be compared with pointer-personality, not comparing the state.
Because they are always stateful.

It's like comparing UIView behavior.

let viewA = UIView()
let viewB = UIView()

viewA == viewB // false

If we do compare with the state structure and data inside, the program might run the wrong way.
So I recommend the developer using a template abstract class to create ViewModel.

/**
 An object as a base class to create an object that provides equatability and hash-value by the pointer personality.
 */
open class StatefulObjectBase: Hashable {

  public final class func == (lhs: StatefulObjectBase, rhs: StatefulObjectBase) -> Bool {
    lhs === rhs
  }

  public func hash(into hasher: inout Hasher) {
    __identifier.hash(into: &hasher)
  }

  private var __identifier: ObjectIdentifier!

  public init() {
    self.__identifier = ObjectIdentifier(self)
  }
}

#if canImport(DifferenceKit)
import DifferenceKit

extension StatefulObjectBase: Differentiable {
  public var differenceIdentifier: ObjectIdentifier {
    self.__identifier
  }
}
#endif