Tag support in Interface Builder for custom NSViews

NSView+CustomTaggable.swift

//
//  NSView+CustomTaggable.swift
//  
//  Allows you to set tags in Interface Builder for custom NSViews.
//
//  Usage:
//
//  Your custom view must implement the CustomTaggable protocol. Then, in your custom
//  NSView, declare the customTag property like this:
//
//  @IBDesignable
//  class MyView: NSView, CustomTaggable
//  {
//    @IBInspectable var customTag:Int = -1
//    //…
//  }
//
//  Ideally, Apple should allow custom NSViews to have regular tags set for them in IB.
//
//  Please dupe this radar if you agree: rdar://21888110
//  (View text of radar on Open Radar at http://openradar.appspot.com/21888110)
//
//  Created by Aral Balkan on 18/07/2015.
//  Copyright (c) 2015 Ind.ie. Released under the MIT License.
//

import Cocoa

extension NSView
{
    func viewWithCustomTag(customTag:Int) -> NSView?
    {
        //
        // Iterates over subviews and returns the view with the specified custom tag.
        // The custom view must implement the CustomTaggable protocol.
        //
        for view in subviews
        {
            if let view = view as? NSView, customTaggableView = view as? CustomTaggable
            {
                if customTaggableView.customTag == customTag
                {
                    return view
                }
            }
        }
        return nil
    }
}

protocol CustomTaggable
{
    var customTag:Int {get set}
}