Swift 4 is the latest version release of Apple. Its main focus is to provide compatibility with Swift 3. It has most changes that are fully compatible with your existing swift code. Swift 4 has a new protocol that serializes and deserializes custom data types without writing any codes. It also introduces new multi-line string literal syntax, which adds line breaks freely.
Swift 4 has many new features such as
1. Improved key path for key-value coding
2. Improved dictionary functionality
3. One sided ranges