AccessibilityModel.swift

import UIKit

protocol AccessibilityModel {
  
  /// Whether the view should be an accessibility element
  var isAccessibilityElement: Bool { get }
  
  /// An optional accessibility label. This is read out by VoiceOver as
  /// soon as the VoiceOver cursor focuses on the accessibility element.
  ///
  /// It is recommended to provide at least an accessibility label when
  /// setting `isAccessibilityElement` to `true`.
  var accessibilityLabel: String? { get }
  
  /// An optional accessibility hint. This is read out by VoiceOver a
  /// moment after the accessibility label has been read out (and traits if set).
  ///
  /// Accessibility hints are a great place to provide further information
  /// about what the accessibility element represents or does.
  ///
  /// Do not put vital information in hints, because they can be disabled by
  /// the user.
  var accessibilityHint: String? { get }
  
  /// An optional accessibility identifier. This is not read out by VoiceOver
  /// but can be used to select and identify accessibility elements, useful
  /// for UI testing.
  var accessibilityIdentifier: String? { get }
  
  /// Accessibility traits represent the various traits that characterise
  /// an accessibility element. Accessibility traits can be combined, if
  /// required, and are read out by VoiceOver before or after the accessibility label is
  /// read out, depending on the trait.
  ///
  /// Set traits that make sense for the type of element you’re defining.
  /// For example, a selected selectable cell could have the traits
  /// UIAccessibilityTraitButton and UIAccessibilityTraitSelected.
  /// and a UILabel could have the trait UIAccessibilityTraitHeader.
  var accessibilityTraits: UIAccessibilityTraits { get }
  
}

/// Make each property optional by giving it a default implementation in
/// a protocol extension.
extension AccessibilityModel {
  
  var isAccessibilityElement: Bool {
    return false
  }
  var accessibilityLabel: String? {
    return nil
  }
  var accessibilityHint: String? {
    return nil
  }
  var accessibilityIdentifier: String? {
    return nil
  }
  var accessibilityTraits: UIAccessibilityTraits {
    return UIAccessibilityTraitNone
  }
  
}