swiftui_state_tests.swift

import SwiftUI

class Base: CustomDebugStringConvertible {
  var debugDescription: String {
    "\(type(of: self)) \(ObjectIdentifier(self))"
  }

  init() {
    print("🟢 init\t", self)
  }

  deinit {
    print("🔴 deinit", self)
  }
}

final class A: Base {}
final class B: Base {}
final class C: Base {}

enum E {
  enum Kind: Equatable {
    case a
    case b
    case c

    var next: Kind {
      switch self {
      case .a:
        return .b
      case .b:
        return .c
      case .c:
        return .a
      }
    }
  }

  case a(A)
  case b(B)
  case c(C)

  var kind: Kind {
    switch self {
    case .a:
      return .a
    case .b:
      return .b
    case .c:
      return .c
    }
  }

  var base: Base {
    switch self {
    case .a(let a):
      return a
    case .b(let b):
      return b
    case .c(let c):
      return c
    }
  }
}

struct Parent: View {
  @State
  private var _kind: E.Kind = .a

  private func _initE() -> E {
    switch _kind {
    case .a:
      return .a(A())
    case .b:
      return .b(B())
    case .c:
      return .c(C())
    }
  }

  var body: some View {
    VStack {
      Child(_initE())
      Button("Inject next E:") {
        print("\n🔸 Button action:\n")
        self._kind = self._kind.next
      }
    }
  }
}

struct Child: View {
  @State
  private var _e: E

  init(_ e: E) {
    self.__e = State(wrappedValue: e)
    print("Child init call:")
    dump(__e)
  }

  var body: some View {
    print("Child body call:")
    dump(__e)
    return Text(_e.base.debugDescription)
  }
}

struct TestCase_PreviewProvider: PreviewProvider {
  static var previews: some View {
    Parent()
  }
}