title: Concat String and convert them to &str
body: <pre><code>fn lyrics_more_bottles(song_template: &amp;mut String, number: i32) {
      let mut template_partials = HashMap::new();
      let mut start_num = number.to_string();
      let mut remaining_num = (number - 1).to_string();
  
      template_partials.insert("start", start_num + " bottles");
      template_partials.insert("repeat", start_num + " bottles");
      template_partials.insert("remaining", remaining_num + " bottles");
      template_partials.insert("message", "Take one down and pass it around");
  
      resolve_template(song_template, template_partials);
  }
  </code></pre>
  
  <p>I can't manage to convert those concatenated strings to a <code>&amp;str</code>. I tried to put them into parentheses and call <code>.as_str()</code>. No luck on that. </p>
  
  <p>I need to have a <code>HashMap&lt;&amp;str, &amp;str&gt;</code> so having a <code>String</code> is not an option here.</p>