title: How can I initialize a mixin's immutable data in Dart?
body: <p>I am programming in Flutter using Dart 2.1.0, and come across this situation:</p>
  
  <pre><code>mixin Salt {
    final int pinches;  // Immutable, and I want to delay initialization.
  
    // Cannot declare constructors for mixin
  }
  
  class Meat with Salt {
    Meat(int pinches) ... // How to initialize it?
  }
  </code></pre>
  
  <p><code>Salt</code> has no constructor, so I cannot use initializer list. <code>pinches</code> is <code>final</code>, so I cannot set it in <code>Meat</code>'s constructor.</p>
  
  <p>I don't want to make <code>Salt</code> a class because <code>Meat</code> may need to extend from something else.</p>
  
  <p>And I want to keep <code>pinches</code> immutable.</p>
  
  <p>Any way to do it? Thanks in advance.</p>