title: What's the purpose of PHP7's returning values type declaration
body: <p>I'm reading the new features of PHP7 and this doubt comes to me with this one:</p>
  
  <p><a href="http://php.net/manual/en/functions.returning-values.php#functions.returning-values.type-declaration" rel="nofollow noreferrer">Returning values: Return type declarations</a></p>
  
  <pre><code>function sum($a, $b): float {
      return $a + $b;
  }
  
  // Note that a float will be returned.
  var_dump(sum(1, 2));
  </code></pre>
  
  <p>The only purpose I can find is to be more specific in interface definition (which is an advantage). But, is there any other reason of including them in every method?</p>