typealias in class vs in function in swift (iOS)

Question

1. What's the difference between a typealias declaration in class vs its declaration inside a function?

2. Is there any performance detail?

3. Is it a good idea to use them inside functions?

Answer 1

1. The difference is just the scope. A declaration inside a function hides one from outside.

2. Since this is handled all by the compiler it has nothing to do with performance.

3. Use it, where it makes sense (from a scope view)