There are a number of issues with Swift, though I&#x27;m sure they will improve:<p>1) No backwards compatibility: developers must keep rewriting their Swift code with each new Swift release, since syntax and features often change.<p>2) Swift&#x27;s interaction with C++ is a non-starter, and many, many apps use C++.<p>3) Some C APIs are still quite difficult to use from Swift. Objective-C, being a strict superset of C, makes it very easy to use Core Audio, for instance. OpenGL interop can also be a bit frustrating.<p>4) Swift&#x27;s &quot;functional&quot; idioms are weak and poorly implemented. If you can&#x27;t provide a true functional backdrop to these features, they probably shouldn&#x27;t even be in there. Coming from a real functional language, you&#x27;re in for nasty surprises in Swift if you casually use higher-order functions all over the place, because there is a lot of copying going on.<p>5) Swift&#x27;s performance is definitely not, shall I say, &quot;swift,&quot; though hopefully that will eventually improve.<p>6) Poor and confusing compiler errors.<p>I actually realize now that I could go on all day about this.