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What are the changes in Swift 3?

Paul Hudson       @twostraws

Swift 3.0 introduced the biggest changes to the language since it was released, and it’s 100% guaranteed to cause your current code to break unless you had written some extraordinarily trivial apps.

I went over the changes in more detail in my article What’s new in Swift 3.0?, but here are the headline changes:

  • All function parameters have labels unless you request otherwise.
  • Needless or duplicated words in method names have been removed.
  • UpperCamelCase has been replaced with lowerCamelCase for enums and properties.
  • C functions from Core Graphics and GCD have been replaced with method syntax.
  • Everything deprecated in Swift 2.2 has now been removed from the language.
  • Closures are now considered to be non-escaping by default; if you need them to escape you need to use the new @escaping attribute.
  • Key paths (for KVO) can now be specified using the #keyPath directive.
  • Many Foundation types have been converted to structs; most have dropped their “NS” name prefix.
  • Many closure parameters now have default values, so you don’t need to write completion: nil much any more.

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