Swift Style

Nesting Functions

Swift allows you to embed functions within each other. This encapsulates the embedded function and allows you to refactor otherwise repeating or abstractable code to a single call point. The Swift compiler is smart enough to inline and optimize these calls as needed.

Here’s an example of a nested function from Swift Foundation:

open class JSONSerialization : NSObject {
  /// Determines whether the given object can be
  /// converted to JSON.
  open class func isValidJSONObject(_ obj: Any) -> Bool {
    func isValidJSONObjectInternal(_ obj: Any) -> Bool {
      // Object is Swift.String or NSNull
      if obj is String || obj is NSNull {
        return true
      }
      ...

When deciding whether to ...