title: Generic Template String like in Python in Dart
body: <p>In python, I often use strings as templates, e.g.</p>
  <pre class="lang-dart prettyprint-override"><code>templateUrl = '{host}/api/v3/{container}/{resourceid}'  
  params = {'host': 'www.api.com', 'container': 'books', 'resourceid': 10}  
  api.get(templateUrl.format(**params))  
  </code></pre>
  <p>This allows for easy base class setup and the like. How can I do the same in dart?</p>
  <p>I'm assuming I will need to create a utility function to parse the template and substitute manually but really hoping there is something ready to use.</p>
  <p>Perhaps a TemplateString class with a <code>format</code> method that takes a <code>Map</code> of name/value pairs to substitute into the string.</p>
  <p>Note: the objective is to have a generic &quot;format&quot; or &quot;interpolation&quot; function that doesn't need to know in advance what tags or names will exist in the template.</p>
  <p>Further clarification: the templates themselves are not resolved when they are set up. Specifically, the template is defined in one place in the code and then used in many other places.</p>