ReflectSuperclasses.swift

import Foundation
import UIKit

/// Some helpers for having nice test assertions.
public func expectationFailure(
  _ reason: String,
  trace message: String) {
  print(reason, terminator: reason == "" ? "" : "\n")
  print(message, terminator: message == "" ? "" : "\n")
}

public func expectNil<T>(_ value: T?,
  _ message: @autoclosure () -> String = "",
  file: String = #file, line: UInt = #line) {
  if value != nil {
    expectationFailure(
      "expected optional to be nil\nactual: \"\(value!)\"", trace: message())
  }
}

@discardableResult
public func expectNotNil<T>(_ value: T?,
  _ message: @autoclosure () -> String = "",
  file: String = #file, line: UInt = #line) -> T? {
  if value == nil {
    expectationFailure("expected optional to be non-nil", trace: message())
  }
  return value
}

public func expectTrue(_ actual: Bool,
  _ message: @autoclosure () -> String = "",
  file: String = #file, line: UInt = #line) {
  if !actual {
    expectationFailure("expected: true", trace: message())
  }
}

public func expectEqualTest<T>(
  _ expected: T, _ actual: T,
  _ message: @autoclosure () -> String = "",
  file: String = #file, line: UInt = #line, sameValue equal: (T, T) -> Bool
) {
  if !equal(expected, actual) {
    expectationFailure(
      "expected: \(String(reflecting: expected)) (of type \(String(reflecting: type(of: expected))))\n"
      + "actual: \(String(reflecting: actual)) (of type \(String(reflecting: type(of: actual))))",
      trace: message()
    )
  }
}

public func expectEqual<T : Equatable>(_ expected: T, _ actual: T,
  _ message: @autoclosure () -> String = "",
  file: String = #file, line: UInt = #line) {
  expectEqualTest(expected, actual, message()) {$0 == $1}
}

/// This is the class we will apply reflection to.
class CustomCell : UITableViewCell {
}

/// Perform reflection from bottom to top and assert that NSObject is the maximal in this class hierarchy lattice.
let customCell = Mirror(reflecting: CustomCell())
expectTrue(customCell.subjectType == CustomCell.self)
if let tableViewCell = expectNotNil(customCell.superclassMirror) {
  expectTrue(tableViewCell.subjectType == UITableViewCell.self)
  if let view = expectNotNil(tableViewCell.superclassMirror) {
    expectTrue(view.subjectType == UIView.self)
    if let responder = expectNotNil(view.superclassMirror) {
      expectTrue(responder.subjectType == UIResponder.self)
      if let object = expectNotNil(responder.superclassMirror) {
        expectTrue(object.subjectType == NSObject.self)
        expectNil(object.superclassMirror)
      }
    }
  }
}