title: Concat Flux with its count (or another reduce function)
body: <p>Is it possible to proceed(concat) a Flux with some reduce function on it, for example number of passed elements?</p>
  <p>That is, for example, to turn a</p>
  <pre><code>Flux.fromStream(Stream.of(&quot;a&quot;, &quot;b&quot;, &quot;c&quot;)) //note source flux could be read only once 
  </code></pre>
  <p>to Flux that will evaluate in</p>
  <pre><code>&quot;a&quot;, &quot;b&quot;, &quot;c&quot;, &quot;3&quot;
  </code></pre>