Open Radar

 
Summary:
Non-idiomatic Swift in the SceneKit template makes it easy to introduce a run time crash when modifying the template.

Steps to Reproduce:
1. Create a new project using the Game template specifying Swift and SceneKit

2. Change this code so that it searches for a different node instead of “ship” and then animates it:

    // retrieve the ship node
    let ship = scene.rootNode.childNodeWithName("ship", recursively: true)
    
     // animate the 3d object
     ship.runAction(SCNAction.repeatActionForever(SCNAction.rotateByX(0, y: 2, z: 0, duration: 1)))

The only thing you need to change is the string “ship”, the animate line is included for context because that’s where the crash occurs. Note that a good reason to do search for a different node is you are using a different .dae file or constructing the scene yourself, but you do not need to do this to see the bug.

3. Build and run

Expected Results:
It finds nothing and doesn’t animate the ship

Actual Results:
Runtime crash with message “fatal error: unexpectedly found nil while unwrapping an Optional value”

Regression:
None

Notes:
To fix, change the code to this:
    // retrieve the ship node
    if let ship = scene.rootNode.childNodeWithName(“ship”, recursively: true) {
        // animate the 3d object
        ship.runAction(SCNAction.repeatActionForever(SCNAction.rotateByX(0, y: 2, z: 0, duration: 1)))            
    }
This will not crash even if the node is not found, and while my knowledge of Swift is limited I think this is the best way to do it. It’s possible that a root cause is that SceneKit should return an optional (?) instead of explicitly unwrapped (!) node, but I’m still figuring that stuff out.