title: Constant constructor in Dart (Flutter)
body: <p>Can someone explain, what the advantages of constant constructors are? If I have a StatefulWidget</p>
  <pre><code>class X extends StatefulWidget {
    const X(this.a, this.b,...);
    A a;
    B b;
  ...
  }
  </code></pre>
  <p>I do not understand why <code>const</code> is used. If I understand correctly, <code>const</code> means it is known at compile time, but what is it for? Usually the attributes <code>a</code>, <code>b</code>, etc. are not known at compile time, but at runtime, so what is the point for the <code>const</code> constructor?</p>