title: Defining Memcache as Symfony service produces unhelpful error
body: <p>I'm trying to define Memcache as a service in Symfony 3.4 and it doesn't appear to want to work.</p>
  
  <p>This has previously worked correctly with a Symfony 2 build which is where the configuration is taken from.</p>
  
  <p>I've got the following code in my services.yml:</p>
  
  <pre><code>memcache:
      class: \Memcache
      arguments:
        persistent_id: elearn
      calls:
        - [ addServer, [ %memcached_host%, %memcached_port% ]]
  </code></pre>
  
  <p>However when attempting to clear the Symfony cache I'm getting the following error:</p>
  
  <pre><code>In AbstractRecursivePass.php line 126:
  
  Invalid service "memcache": class "\Memcache" has no constructor.
  </code></pre>
  
  <p>This would make sense to me if we were trying to pass some constructor arguments in the service definition, as, like it says Memcache has no constructor but clearly we aren't doing that.</p>
  
  <p>Am I missing something obvious?</p>