obj?.fn() calls fn member function if the object isn’t null, otherwise doesn’t do anything. obj!.fn() on the other hand asserts that obj isn’t null, and calls fn. If the object is null, you get an exception. So it’s a difference in assertiveness: you either ask or simply claim the nullable property of a nullable object.
The error message is quite clear. You cannot declare an extension inside of anything – inside a class declaration, inside a struct declaration, etc. It must be outside of everything, at the top level of the containing file. There must be no curly braces around it. You have not shown the context in which you are declaring this extension, but clearly there are curly … Read more
It’s been a few weeks since I posted this, but I believe what Aaron Brager said is true. While Protocol-Oriented-Programming is rather new in itself, the idea of protocols has been present in Objective-C for a long time, they are in Swift, and they have their variants in languages such as Java. Due to the … Read more