title: FBLPromise crash with CocoaPods and SwiftPM implemented in both
body: <p>We've been migrating away from CocoaPods since a while, but not every dependency has made the switch. <a href="https://github.com/firebase/firebase-ios-sdk/issues/3136" rel="nofollow noreferrer">Like Firebase</a>.</p>
  
  <p>I've had a similar question <a href="https://stackoverflow.com/questions/60002257/duplicate-symbols-with-cocoapods-and-swiftpm">regarding duplicate symbols</a>, but now I'm facing something new, which is probably because I'm using a dependency in both SwiftPM as in CocoaPods.</p>
  
  <p>After running my (sample) project it crashes:</p>
  
  <pre><code>-[FBLPromise firebaseInstallationID]: unrecognized selector sent to instance 0x600003f5a430
  </code></pre>
  
  <p>with a warning at the top:</p>
  
  <pre><code>objc[93047]: Class FBLPromise is implemented in both
  /xxx/SampleProject.app/Frameworks/FBLPromises.framework/FBLPromises (0x10b3f09a8) and 
  /xxx/SampleProject.app/SampleProject (0x10af736f0).
  One of the two will be used. Which one is undefined.
  </code></pre>
  
  <p>Prior to my update to Firebase SDK v6.26.0 I would only get the first warning, but since the update it crashes.</p>
  
  <p>I saw a doc about how to use <a href="https://github.com/firebase/firebase-ios-sdk/blob/master/docs/firebase_in_libraries.md" rel="nofollow noreferrer">Firebase within libraries</a> and a <a href="https://github.com/firebase/firebase-ios-sdk/issues/5467" rel="nofollow noreferrer">GitHub issue</a> regarding a similar crash. But nothing seems to work to resolve this crash, other then downgrading.</p>
  
  <p>I uploaded a sample project: <a href="https://github.com/basvankuijck/SampleProjectFirebaseCrash" rel="nofollow noreferrer">https://github.com/basvankuijck/SampleProjectFirebaseCrash</a>.</p>
  
  <p>Removing the SwiftPM Promises dependency is not an option, since the actual project is using a SwiftPM dependency that has a dependency to Promises. </p>
  
  <p>The <a href="https://github.com/basvankuijck/SampleProjectFirebaseCrash/blob/master/Podfile" rel="nofollow noreferrer">Podfile</a> is nothing that fancy, and the SampleProject just uses <a href="https://github.com/basvankuijck/SampleProjectFirebaseCrash/blob/master/SampleProject.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved" rel="nofollow noreferrer">one single SwiftPM dependency</a>.</p>
  
  <p>Anyone who has an idea how to let SwiftPM and CocoaPods play nicely together especially with Firebase in the middle?</p>