title: Swift: dynamic strings with local variable injections
body: <p>Not sure if this is possible. But I want to do this:</p>
  
  <pre><code>let version = "2.0.1"
  let year = 2017
  let version = "Build \(version), \(year)"
  </code></pre>
  
  <p>However, I want to source the version string from a localised file. ie.</p>
  
  <pre><code>let version = "2.0.1"
  let year = 2017
  let versionTemplate = NSLocalizedString("version.template", comment:"")
  let version = ???? // Something done with versionTemplate
  </code></pre>
  
  <p>I've looked at using <code>NSExpression</code>, but it's not obvious if it can do this or how.</p>
  
  <p>Anyone does this?</p>