title: error while setting conditional value in rust using format in string
body: <p>I have an issue related to conditional value to a string in rust, if I remove format() everything runs fine but I have no idea how to implement this with format.</p>
  <pre><code> let value =
                      if matcha.sugar {
                          format!(&quot;Hello {} your matcha is ready at {}ºC with sugar&quot;, self.client, matcha.temp);
                      }
                      else {
                          format!(&quot;Hello {} your matcha is ready at {}ºC without sugar&quot;, self.client, matcha.temp);
                      }.to_string();
  </code></pre>
  <p>Error Message:</p>
  <pre><code>    &quot;message&quot;: &quot;the method `to_string` exists for unit type `()`, but its trait bounds were not satisfied\n\nmethod cannot be called on `()` due to unsatisfied trait bounds\n\nnote: the following trait bounds were not satisfied:\n      `(): std::fmt::Display`\n      which is required by `(): std::string::ToString`&quot;,
      &quot;source&quot;: &quot;rustc&quot;,
      &quot;relatedInformation&quot;: [
          {
              &quot;startLineNumber&quot;: 60,
              &quot;startColumn&quot;: 23,
              &quot;endLineNumber&quot;: 60,
              &quot;endColumn&quot;: 32,
              &quot;message&quot;: &quot;method cannot be called on `()` due to unsatisfied trait bounds&quot;,
              
          }
      ]
  }]
  </code></pre>