title: Dart: const variables must be initialized with a constant value
body: <p>Why there is an error, when the <code>foo</code> is already a <code>const</code> value?</p>
  
  <pre><code>const foo = const [10, 20];
  const bar = foo[0] * 2; // error: const variables must be initialized with a constant value. 
  </code></pre>