title: How to use restricted mixin to an interface with implementation of that interface at same time in dart?
body: <p>What I have:</p>
  <ol>
  <li>Interface (InterfaceA) with a method that must be overridden.</li>
  <li>Restricted to interface mixin (MixinB) with a method that I want to use without overriding.</li>
  <li>Class (ClassC) with implementation of interface and usage of mixin.</li>
  </ol>
  <p>Question:
  Is it possible to use restricted mixin to interface with implementation of that interface at the same time?</p>
  <p>Code below is an example and shows how I ideally want to use mixin and interface</p>
  <pre class="lang-dart prettyprint-override"><code>abstract class InterfaceA {
    int getValue();
  }
  
  mixin MixinB on InterfaceA {
    int getPreValue(int i) =&gt; i;
  }
  
  // Error:
  // 'Object' doesn't implement 'InterfaceA' so it can't be used with 'MixinB'.
  class ClassC with MixinB implements InterfaceA {
    @override
    getValue() =&gt; getPreValue(2);
  }
  </code></pre>