title: What does "missing lifetime specifier" mean when storing a &str in a structure?
body: <p>I am trying to code an Excel-like data structure:</p>
  
  <pre><code>use std::collections::HashMap;
  
  struct Excel {
      columns: HashMap&lt;&amp;str, Vec&lt;f64&gt;&gt;,
  }
  
  fn main() {}
  </code></pre>
  
  <p>but I am getting an error:</p>
  
  <pre class="lang-none prettyprint-override"><code>error[E0106]: missing lifetime specifier
   --&gt; src/main.rs:4:22
    |
  4 |     columns: HashMap&lt;&amp;str, Vec&lt;f64&gt;&gt;,
    |                      ^ expected lifetime parameter
  </code></pre>
  
  <p>Can someone help me understand what's going on?</p>