Swift version: 5.1
Swift 2.0 introduced a lot of major language changes. You can read my full article explaining the changes with code examples by clicking here, but here are the highlights:
guardkeyword to check input while unwrapping optionals
characters.count(Note: this was later un-done in Swift 4.)
performSelector()family of functions is now available
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Available from iOS 7.0
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.