View GLKit objects in Debug in Swift project

The GLKit maths structures are imported from C, and the C types are declared quite weirdly. For example,

GLKVector4

union _GLKVector4

union _GLKVector4
{
    struct { float x, y, z, w; };
    struct { float r, g, b, a; };
    struct { float s, t, p, q; };
    float v[4];
} __attribute__((aligned(16)));

Swift deals with this surprisingly well, but it’s clear that it doesn’t emit enough debugging metadata to allow the debugger to display the contents nicely.

You should definitely file a bug about this; please post your bug number, just for the record.

In terms of workarounds, there’s a bunch of possibilities:

• It may be possible to work around this using a summary format (control click on the variable in the debugger to see the editor for that). Alas, I wasn’t able to get that to work in a Swift context.

• You can definitely view the values as a custom type:

  1. Select the variable in the debugger.

  2. Control click and choose View Value As > Custom Type.

  3. Enter a custom type. To continue my

     GLKVector4

     example, this would be

     (v.x, v.y, v.z, v.w)

     .

  4. In the new item, click the disclosure triangle to see the elements.

• You can print the variable in the debugger console:

  (lldb) p v.x
  (Float) $R10 = 1
  (lldb) p v.y
  (Float) $R12 = 2
  (lldb) p v.z
  (Float) $R14 = 3
  (lldb) p v.w
  (Float) $R16 = 4

  That’s a bit cumbersome, so one option is to extend the type with your own

  CustomDebugStringConvertible

  implementation:

  extension GLKVector4 : CustomDebugStringConvertible {
      public var debugDescription: String {
          return "(\(self.x), \(self.y), \(self.z), \(self.w))"
      }
  }

  You can then print it all at once (using

  po

  , not

  p

  ):

  (lldb) po v
  (1.0, 2.0, 3.0, 4.0)

  .

There may be even better options I haven’t thought of, so I’m looking forward to see if anyone else follows up with some alternative suggestions.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Thank you for the detailed response. I forgot to mention that I was testing this in 9.4.1. I since have upgraded to 10.0 abd found that the issue is still there. I have reported this as a bug here:

https://bugreport.apple.com/web/?problemID=44685031

For now I can use the immediate window to print the contents.