Supporting compactMap in Swift 4

Swift 4.1 is shipping soon with many wonderful things! One of the changes that may affect you is usage of flatMap to remove nil from your Sequence.

let names = ["Maria", nil, "Daniel"]
names.flatMap { $0 } //=> ["Maria", "Daniel"]

Backwards Compatibility

I wanted to ensure I avoided dealing with migration errors/assistant as much as possible. Lucky for us, Swift is a powerful language. We can define an extension Sequence.compactMap for any version below 4.1 🎉.

#if swift(>=4.1)
// This will be provided by the stdlib
#else
  extension Sequence {
    func compactMap<T>(_ transform: (Self.Element) throws -> T?) rethrows -> [T] {
      return try flatMap(transform)
    }
  }
#endif

With the extension in place, we can change our usage of .flatMap { $0 } to .compactMap { $0 } 🤓.