Quickies for Swift

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General

• BNRTimeBlock in Swift [permalink]
  This blog post has a little snippet for timing a block. Here's a Swift version:

  func BNRTimeBlock(_ block: @noescape () -> Void) -> TimeInterval {
      var info = mach_timebase_info()
      guard mach_timebase_info(&info) == KERN_SUCCESS else { return -1 }
      
      let start = mach_absolute_time()
      block()
      let end = mach_absolute_time()
      
      let elapsed = end - start
      
      let nanos = elapsed * UInt64(info.numer) / UInt64(info.denom)
      return TimeInterval(nanos) / TimeInterval(NSEC_PER_SEC)
  }
  

  And call it like

  let time1 = BNRTimeBlock {
      print("groovy")
      // do other work.
  }
  
  print("    took (time1)")
  

• Printable description from Swift thingies [permalink]
  Tired of default output from your objects when doing a sanity-check print?

  Just adopt CustomStringConvertible and implement description:

  extension Weight: CustomStringConvertible {
      var description: String {
          return "(pounds) lbs"
      }
  }
  

  If you're inheriting from NSObject, then you actually already have a description method, and will get an error to the tune of "redundant conformance of blah blah blah". In that case, you'd do this:

  extension IndoorCyclingClass {
      override var description: String {
          return "(title) - (classDescription)"
      }
  }
  

• Swift if case let [permalink]
  Because I can never remember the syntax: Given

  enum FilterOptionValue {
      case oneSided(value: Double)
      case twoSided(low: Float, high: Double)
  }
  

  You can unpack it piecewise on demand with

          if case let .twoSided(low, high) = thingieOption.value {
              minThingie = Int(low)
              upperThingie = Int(high)
          }
  

Hacks

• #if 0 in Swift [permalink]
  Have a bunch of code to temporarily chop out because of reasons? In C you could use #if 0 to tear out chunk of your file.

  #if in Swift generally requires the guts of the conditional to be syntactically correct (even if it's semantically nonsense).

  You can abuse the Swift version check to do something similar to #if 0:

       ...
  #if swift(>=666)
      aj2n42j4n23jnjsdnfjsnfjnunrun unr unwu nudjfn jsnf jn
      var window: UIWindow?
  #endif
     ...
  

  The compiler still does some processing of the code, so you might get an error (like if that cat-stomp at the beginning started with a digit, Swift tries interpreting 2n42j4n23jnjsdnfjsnfjnunrun as an integer literal and fails)

  (Thanks to Jeremy Sherman for the idea)

Random

• Doing Notifications Swiftstyle [permalink]
  Posting end

     NotificationCenter.default.post(name: Notification.Name("FishBattery"), object: tour)
  

  Receiving end

  NotificationCenter.default.addObserver(
      forName: Notification.Name("FishBattery"),
      object: tour,
      queue: OperationQueue.main) { [weak self] notification in
          guard let tour = notification.object as? Tour else {
              return
          }
          if tour == self?.tour {
              self?.uploadIfNeeded()
          }
      }
  

lldb

• Running swift code in LLDB [permalink]
  

  (lldb) expr -l swift -- let $ook = "verb"
  (lldb) expr -l swift -- print("I seem to be a ($ook)")
  I seem to be a verb
  

  And if you want to call your own stuff (say the project name is C-Interop):

  (lldb) expr -l swift -- import C_Interop
  (lldb) expr -l swift -- SomeClass().useAnother()
  

  This creates a new instance of SomeClass and calls the useAnother method.

  (Thanks to Zach Waldowski for this one.)

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