title: What are template deduction guides and when should we use them?
body: <p>The C++17 standard introduces "template deduction guides". I gather they're something to do with the new template argument deduction for constructors introduced in this version of the standard, but I haven't yet seen a simple, FAQ-style explanation of what they are and what they're for.</p>
  
  <ul>
  <li><p>What are template deduction guides in C++17?</p></li>
  <li><p>Why (and when) do we need them?</p></li>
  <li><p>How do I declare them?</p></li>
  </ul>