title: Adding method to library
body: <p>I've been recently writing simple game in C++ with SFML. Here's my question:</p>
  
  <p>In SFML library there is a template class <code>Vector2&lt;T&gt;</code> (specifically I'd be using <code>Vector2f</code>). Unfortunately, it doesn't have any method to rotate itself, so I came with the idea to write one. But as I wrote:</p>
  
  <pre><code>template&lt;typename T&gt; void Vector2&lt;T&gt;::Rotate(float a);
  </code></pre>
  
  <p>the compiler says that I can't do things like this:</p>
  
  <pre><code>printable.h:31:53: error: no ‘void sf::Vector2&lt;T&gt;::Rotate(float)’ member function declared in class ‘sf::Vector2&lt;T&gt;’
  </code></pre>
  
  <p>Is it possible to add custom method like this? Or should I wrap Vector2f into my own class?</p>