stevecass

import UIKit

let nonOptionalVar: [String] = ["a", "b", "c"]
let optionalVar:String? = "jimmy"

// this compiles OK with import UIKit present
let ex1: [String: AnyObject] = ["key" : nonOptionalVar, "notherkey": ["content": optionalVar!]]

// Here we forget the ! character that unwraps the optional
// error: contextual type 'AnyObject' cannot be used with dictionary literal

stevecass

class Post < ActiveRecord::Base
  has_many :comments, as: :commentable
end

class Photo < ActiveRecord::Base
  has_many :comments, as: :commentable
end

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true