title: auto specifier in header file
body: <p>I have a file <code>Foo.h</code>:</p>
  <pre class="lang-cpp prettyprint-override"><code>// Foo.h
  #pragma once
  
  int foo();
  </code></pre>
  <p>Also I have a <code>Foo.cpp</code> file which implements <code>Foo.h</code>:</p>
  <pre class="lang-cpp prettyprint-override"><code>//Foo.cpp
  #include &quot;Foo.h&quot;
  
  int foo() {
      return 5;
  }
  </code></pre>
  <p>Is there a way to make <code>foo</code> function return type <code>auto</code>? It may be useful if I create a function which return value depends on 3rd party library functions, which return value types may change in later versions.</p>