What are the changes in Swift 3?

Swift version: 5.1

Paul Hudson @twostraws May 28th 2019

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.