I find that the incremental building with the Swift compiler sometimes creates executables that jump to the wrong method.
I am guessing the calling site didn't realise the called class has a new method and the tables are wrong.
The only way to fix this from Xcode is with a clean. - But clean also nukes asset catelogs. And my asset catelogs take an age to compile.
Is there a smart way to **** the code and leave the catelogs in place?