title: Dart Map syntax: putIfAbsent('FirstKey',() => 1); What is: ()?
body: <p>In editor hint you get:      </p>
  
  
  
  <pre class="lang-dart prettyprint-override"><code>scores.putIfAbsent(key, () =&gt; numValue);
  </code></pre>
  
  <p>I am adding single "rows" to my Maps with commands: </p>
  
  <pre class="lang-dart prettyprint-override"><code>myMap.putIfAbsent(9, () =&gt; 'Planned');
  yourMap.putIfAbsent('foo', () =&gt; true);
  </code></pre>
  
  <p>so: what does that  ()   mean ?</p>