Open Radar

 
Summary:
Free yourself from the tyranny of animation completion blocks to handle order out of sublayers

Steps to Reproduce:
I describe relative animation of Core Animation sublayers as mathematical sets. Instead of using animation completion blocks to handle animating sublayers and order out, you should animate them relatively: old minus new to zero. That means for example when animating sublayers from A-B-C-D to A-B-D, ordering out layer C, old minus new leaves just C. When added back to the model value it gives A-B-D-C. The only requirement is the sublayers must then be sorted.

Expected Results:
Animating sublayers order out without completion blocks. You avoid indeterminate state as everything is done instantly, when the animation starts.

Actual Results:
When you depend on completion handlers, you must reason about all possibilities if interacting while an animation is in progress.

Version:
Not applicable

Notes:
Lots of Mac and iOS apps use blocking, because your engineers have just given up on usability.