title: Rust best practices when specifying a constant hash map
body: <p>I'm trying to set a constant, predefined hash map in Rust.  I'm not sure what the best practice is in Rust for this.</p>
  
  <pre><code>use std::collections::HashMap;
  
  pub const Countries: HashMap&lt;&amp;str, &amp;str&gt; = [
      ("UK", "United Kingdom"),
      ("US", "United States")
  ].iter().cloned().collect();
  </code></pre>
  
  <p>These will then be referenced later in the library.</p>
  
  <p>If this is bad, I'm guessing a match in a function is the best way?</p>