> seamless interop with Objective-C and C The interop actually has lots of seams. A huge engineering effort had to be made and has been made to paper over tho

> seamless interop with Objective-C and C The interop actually has lots of seams. A huge engineering effort had to be made and has been made to paper over those seams, but they are definitely there. Calling conventions are gratuitously incompatible, objects have to be converted at API boundaries at significant cost, the meta-systems are incompatible, etc.