title: Cannot integrate Firebase iOS SDK - Undefined symbols for architecture x86_64:
body: <p>I've been trying to get this <code>SDK</code> installed into my iOS project without much success. </p>
  
  <p>At first, I tried to install it manually, using the setup instructions from here: <a href="https://firebase.google.com/docs/ios/setup#initialize_firebase_in_your_app" rel="noreferrer">https://firebase.google.com/docs/ios/setup#initialize_firebase_in_your_app</a></p>
  
  <p>However, after following the <code>readme</code> file exactly, when I try use this code: </p>
  
  <pre><code>[FIRApp configure];
  </code></pre>
  
  <p>After importing <code>Firebase.h</code> into the header file, it doesn't recognise the <code>FIRApp</code> and the reason seems to me missing files from the framework as <code>FIRApp.h</code> doesn't exist in the headers. </p>
  
  <p>So, I resorted to the much-hated, <code>Cocoapods</code> installation. Everything installs fine and no warnings show during the <code>pod install</code> part. However, again, when I add the following code: <code>[FIRApp configure];</code> I am present with a different error: </p>
  
  <blockquote>
    <p>Undefined symbols for architecture x86_64:<br>
    "_OBJC_CLASS_$_FIRApp", referenced from:
          objc-class-ref in AppDelegate.o</p>
  </blockquote>
  
  <p>For the life of me, I cannot figure this out. I have searched Google and SO with various solutions that haven't helped. </p>
  
  <p>I would like to get it working with Cocoapods as I have done all the leg work with getting it installed now. </p>