title: a class method named ._() function in dart?
body: <p>I've seen this code can anyone please explain to me what the <code>AppTheme._()</code> means, as I've read about its singleton class in dart but I really can't understand how it works.</p>
  
  <pre><code>class AppTheme {
    AppTheme._();
  
    static const Color notWhite = Color(0xFFEDF0F2);
    static const Color nearlyWhite = Color(0xFFFEFEFE);
    static const Color white = Color(0xFFFFFFFF);
    static const Color nearlyBlack = Color(0xFF213333);
  
    ...
  }
  </code></pre>