title: Defining `Thread#initialize`
body: <p>How can I define <code>Thread#initialize</code>? I tried the following:</p>
  
  <p>(1)</p>
  
  <pre><code>class Thread
    def initialize
      super
      @foo = []
    end
  end
  Thread.new{}.join
  </code></pre>
  
  <p>(2)</p>
  
  <pre><code>class Thread
    def initialize &amp;pr
      super(&amp;pr)
      @foo = []
    end
  end
  Thread.new{}.join
  </code></pre>
  
  <p>(3)</p>
  
  <pre><code>class Thread
    def initialize
    end
  end
  Thread.new{}.join
  </code></pre>
  
  <p>but they return an error:</p>
  
  <pre><code>Uninitialized thread - check `Thread#initialize'.
  </code></pre>