title: 'List<T>.ForEach()' and mutability
body: <p>I want to translate all points in a <code>List&lt;T&gt;</code>. This works:</p>
  
  <pre><code>for (int i = 0; i &lt;PolygonBase.Count; ++i) 
  {
      PolygonBase[i] = PolygonBase[i] + MousePos;
  }
  </code></pre>
  
  <p>But using <a href="https://msdn.microsoft.com/en-us/library/bwabdf9z%28v=vs.110%29.aspx" rel="nofollow"><code>List&lt;T&gt;.ForEach</code></a> doesn't:</p>
  
  <pre><code>PolygonBase.ForEach(v =&gt; v += MousePos);
  </code></pre>
  
  <p>Ideas?</p>