title: Constant property cannot be initialized in a convenience initializer of a derived class
body: <p>Below is sample code from a playground. What I don't understand is why the <code>b</code> variable in the subclass must be a var type and cannot be a let. Can someone help me understand?</p>
  
  <pre><code>class Base1 {
      init() { }
  }
  
  class Sub1: Base1 {
      let b: Int
  
      override init() {
          super.init()
      }
  
      convenience init(b: Int) {
          self.b = b  // Cannot assign to property: 'b' is a 'let' constant
          self.init()
      }
  }
  </code></pre>