Swift: Banning force unwrapping optionals

Posted: June 28th, 2017 | Author: | Filed under: iOS, macOS, Programming, Swift | Tags: , , , , | No Comments »

Swift Optionals and force unwrapping

The Swift programming language supports optional types, which handle the absence of a value. An optional represents two possibilities: Either there is a value and you can unwrap the optional to access that value, or there isn’t a value at all.

Here is how you can declare an optional variable in Swift:

var myOptionalString: String?

The myOptionalString variable can contain a string value or nil. If the optional has a value, you can access the underlying value by explicitly unwrapping it using the exclamation mark operator like:

print("Underlying value of myOptionalString: \(myOptionalString!).")

Dangers of force unwrapping

Although force unwrapping looks convenient, it is extremely dangerous to use: if the optional has no value and you try to unwrap it, this will trigger a runtime error – generally causing the app to crash.

The majority of crashes I have seen in Swift code have been caused by an incorrect explicit unwrap. Why would someone unwrap a nil optional? There are multiple reasons:

  • An optional variable whose value was never nil becomes nil after a refactoring
  • Code copied and pasted
  • Edge cases where an optional variable is rarely nil

Do what I say, not what I do

Swift documentation

The Swift documentation mentions that you should use force unwrapping with caution in a note:


Force Unwrapping Note

WWDC session 407: Do not abuse forced unwrap

Similarly the session 407 “Understanding Undefined Behavior” of the WWDC 2017 tells us in the slide 125: “Do not abuse forced unwrap”.

Other WWDC sessions abuse forced unwrap

Watch any other session of the WWDC 2017 and you will see a lot (way too much) explicit unwrapping. For example look at the session 203 “Introducing Drag and Drop”. On the slide 120, you can read:

let dragView = interaction.view!

Is this line really safe? Nowhere in the documentation you can read that the UIDragInteraction’s view is guaranteed to have a value. Also if it is guaranteed to have a value, why is it an optional in the API?

Apple’s Sample Code abuse forced unwrap

Download a random Sample Code from Apple Developer website and look if and how force unwrapping is used. For this post I downloaded the latest Swift Sample Code available: Example app using Photos framework. When searching for the explicit unwrapping operator, you can find code like this:


Example app using Photos framework 1

This code assumes that the array of textFields’s alertController contain at least one object. Why not using something much safer like:

alertController.addAction(UIAlertAction(title: NSLocalizedString("Create", comment: ""), style: .default) { _ in
         if let title = alertController.textFields?.first?.text, !title.isEmpty {

Another example in the same project:


Example app using Photos framework 2

Wouldn’t it be cleaner and safer to write instead:

@IBAction func play(_ sender: AnyObject) {
        if let player = playerLayer.player {
            // An AVPlayerLayer has already been created for this asset; just play it.
            player.play()
        } else {

Xcode’s Fix-it wants you to insert the explicit unwrap operator

Xcode’s Fix-it feature proposes to insert the explicit unwrap operator… even when it doesn’t make sense:


Xcode Fix-it

How to avoid forced unwrap

There are multiple solutions that are cleaner and safer than using an explicit unwrap. I also generally find the code more readable. Below are several examples.

Optional Binding (if let)

The following code is correct but uses 2 explicit unwrapping:

if myArray.first?.object != nil && myArray.first!.object!.type == .type1 {
    // Do Something
}

This code is much more readable by using an optional binding:

if let object = myArray.first?.object, object.type == .type1 {
    // Do Something
}

Another similar example which could led to a crash:

myView.setHeight((myLabel?.frame.size.height)!)

Again an if let statement would prevent a possible crash. Note the neat trick of using the same variable name to access the unwrapped value:

if let textLabel = textLabel {
    badgeView.setHeight(textLabel.frame.size.height)
}

Guard statement and multiple optional bindings in a single if statement

Look at the following function. All the errors handling are duplicated code.
Also note the use of the as! operator which can led to a crash if theObject.value is not an NSNumber:

func( object inObject: ObjectType ) {
    if inObject.child!.childType == .childType1 {
        if let theObject = inObject.child!.object(forType: .childType2) {
            if inObject != theObject {
                if let theValue = theObject.value as! NSNumber?, theValue != true {
                    // Do something
                }
                else {
                    // Error handling
                }
            }
            else {
                // Error handling
            }
        }
        else {
            // Error handling
        }
    }
    else {
        // Error handling
    }
}

Instead use an early exit, group the if statements and use the as? operator:

func( object inObject: ObjectType ) {
    guard let child = inObject.child  else {
        return
    }

    if child.childType == .childType1,
        let theObject = child.object(forType: .childType2), inObject != theObject,
        let theValue = theObject.value as? NSNumber, theValue != true {
            // Do something
    } else {
        // Error handling
    }

Nil-Coalescing Operator

Although the following code is safe, it is not elegant:

if newState != nil {
    self.state = newState!
}
else {
    self.state = .default
}

Using the Nil-Coalescing Operator is much cleaner:

self.state = newState ?? .default

Closure expression to initialise member variables

In the following example you might get a crash if myFunc1() is called before myFunc2():

var myObject: MyObject?

func myFunc1() {
    self.myObject = MyObject.init()
}

func myFunc2() {
    self.myObject!.rotate()
}

You can use a closure expression to initialise the variable:

var myObject: MyObject = {
    return MyObject.init()
}()

func myFunc1() {
}

func myFunc2() {
    self.myObject.rotate()
}

Implicit unwrapped optionals

The case of implicit unwrapped optionals is very similar to forced unwrap. From the Swift documentation:

An implicitly unwrapped optional is a normal optional behind the scenes, but can also be used like a nonoptional value, without the need to unwrap the optional value each time it is accessed.

Similarly to force unwrapping an optional, I see a lot of code dangerously using implicit unwrapped optionals. This kind of optionals should also be avoided… except in one case where it is extremely useful: When declaring an IBOutlet, you should use an implicit unwrapped optional because once the method viewDidLoad is called, the IBOutlet will be initialized. Also using the IBOutlet before the viewDidLoad method would be a programming error.

For example you could write:

@IBOutlet weak var myLabel: UILabel!

Conclusion

Apple tells us to use force unwrapping with parsimony. However the explicit unwrap operator is frequently used in the WWDC slides as well as in the sample code. This is saddening because the repetitive usage of force unwrapping by Apple gives bad habits and you can easily forget about the dangers of force unwrapping.

By banning explicit unwrapping in your code, you can make your code safer and avoid a bunch of crashes. Furthermore your code will be more readable and cleaner.


Apple’s use of Swift in iOS 10.1 and macOS 10.12

Posted: November 1st, 2016 | Author: | Filed under: Analysis, iOS, macOS, Programming, Swift | 5 Comments »

Swift has been announced at the WWDC 2014, more than 2 years ago. Most of the sample code projects from Apple are now written in Swift. But does Apple use Swift in iOS 10.1 and macOS 10.12.1?

How to detect if a binary is using Swift?

A na├»ve approach would be to check if an app contains the Swift libraries in its Frameworks folder: libswiftCore.dylib, libswiftFoundation.dylib, …

Here is the content of the Frameworks folder of the MRT.app on macOS 10.12.1
/System/Library/CoreServices/MRT.app/Contents/Frameworks/ :


MRT.app

However this is not a good approach since iOS and macOS contain a private copy of the Swift libraries in /System/Library/PrivateFrameworks/Swift/ . Several apps in iOS and macOS link directly to these system libraries.

Here is the content of the Frameworks folder of the PIPAgent.app on macOS 10.12.1
/System/Library/CoreServices/PIPAgent.app/Contents/Frameworks/ :


PIPAgent.app

A much better approach is to check whether a binary links to a Swift library. This can easily be done with the command line tool ‘otool’ using the -L option:

-L Display the names and version numbers of the shared libraries that the object file uses, as well as the shared library ID if the file is a shared library.

When running this command on the PIPAgent application:

otool -L /System/Library/CoreServices/PIPAgent.app/Contents/MacOS/PIPAgent | grep swift

you would get the following output:

/System/Library/PrivateFrameworks/Swift/libswiftAppKit.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftCore.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftCoreData.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftCoreGraphics.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftCoreImage.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftDarwin.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftDispatch.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftFoundation.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftIOKit.dylib (compatibility version 1.0.0, current version 800.8.18)
/System/Library/PrivateFrameworks/Swift/libswiftObjectiveC.dylib (compatibility version 1.0.0, current version 800.8.18)

Building a script

Using the otool command line tool, it is easy to write a bash function that tells if a file is a binary linked to the Swift libraries:


#------------------------------------------------------------------------
# Function to check if a file (passed as argument $1) is using Swift
# It returns the number of occurrences of the string 'swift'
# from the output of otool
#------------------------------------------------------------------------
isFileUsingSwift ()
{
	otool -L $1 2>/dev/null | grep -o swift | wc -l
}

The processFile bash function takes a file as parameter and will print its path if it’s a binary linked to the Swift libraries:


#------------------------------------------------------------------------
# Function to process a file (passed as argument $1).
# It calls the function isFileUsingSwift() to determine
# if this is a binary using Swift and in this case
# print the path of this file.
#------------------------------------------------------------------------
processFile ()
{
	isFileUsingSwift=$( isFileUsingSwift $1 )
 	if [ ${isFileUsingSwift} != 0 ]
 	then
 		# We found a binary using Swift
	 	echo "   $1"
	fi
}


Looping through all the files of a folder is now a single line:

find ${PATH_TO_CHECK} -type f -exec bash -c 'processFile "$0"' {} \;

Final script

Below is the complete bash script that loops through all the files of a folder and print the paths of all the binaries found that use Swift.
Note: You can download the complete script here.


#!/bin/bash

#---------------------------------------------------------------------
# Bash script that loops through all the files of a folder and
# print the paths of all the binaries found that use Swift
# Created by Alexandre Colucci on 01.11.2016
# http://blog.timac.org/?p=1398
#---------------------------------------------------------------------


#---------------------------------------------------------------------
# Force expand a wildcard pattern into the list of matching pathnames
#---------------------------------------------------------------------
shopt -s nullglob

#---------------------------------------------------------------------
# Function to print the usage
#---------------------------------------------------------------------
printUsage ()
{
	echo "Usage: detectSwift.sh PATH"
	echo "PATH: Folder to search for binaries using Swift"
	echo ""
	echo "Examples:"
	echo "  detectSwift.sh /System/Library"
	echo "  detectSwift.sh /System"
	echo "  detectSwift.sh /"
	echo ""
	echo "Note: run as root in order to avoid permission issues."
	echo ""
}

#---------------------------------------------------------------------
# Function to check if a file (passed as argument $1) is using Swift
# It returns the number of occurrences of the string 'swift'
# from the output of otool
#---------------------------------------------------------------------
isFileUsingSwift ()
{
	otool -L $1 2>/dev/null | grep -o swift | wc -l
}

#---------------------------------------------------------------------
# Function to process a file (passed as argument $1).
# It calls the function isFileUsingSwift() to determine
# if this is a binary using Swift and in this case
# print the path of this file.
#---------------------------------------------------------------------
processFile ()
{
	isFileUsingSwift=$( isFileUsingSwift $1 )
 	if [ ${isFileUsingSwift} != 0 ]
 	then
 		# We found a binary using Swift
	 	echo "   $1"
	fi
}

#---------------------------------------------------------------------
# Check if the script was called with the expected usage
#---------------------------------------------------------------------
PARAMETER_NUMBER=$#
PARAMETER_REQUIRED=1
if [ $PARAMETER_NUMBER != $PARAMETER_REQUIRED ];
then
	printUsage
	exit 1
fi


#---------------------------------------------------------------------
# Get the folder path
#---------------------------------------------------------------------
PATH_TO_CHECK=$1

echo ""
echo "Start time:"
date
echo ""
echo "Apps using Swift in ${PATH_TO_CHECK}"


#---------------------------------------------------------------------
# Export the functions so that the subshell inherits them
#---------------------------------------------------------------------
export -f isFileUsingSwift
export -f processFile

#---------------------------------------------------------------------
# Find all the regular files in all subdirectories
# and call for each the function processFile()
#---------------------------------------------------------------------

find ${PATH_TO_CHECK} -type f -exec bash -c 'processFile "$0"' {} \;


#---------------------------------------------------------------------
# Finalizing
#---------------------------------------------------------------------
echo ""
echo "Completed at:"
date
echo ""

Running the script

The script is really slow: for each regular file it will create a subshell, call otool, grep and wc.
Running this script on the iOS 10.1 filesystem takes around 30 minutes.

For macOS 10.12.1, running the script on / takes dozen of hours. I recommend to only run this script on /System, /Applications and /usr. Processing these 3 folders in parallel will take around 2 hours.

Apple’s use of Swift in iOS 10.1

Running the script on iOS 10.1 (14B72c) of an iPhone 7 Plus will give you this list of binaries:

/Applications/Calculator.app/Calculator
/Applications/Music.app/Music
/Applications/Music.app/PlugIns/MusicMessagesApp.appex/MusicMessagesApp
/Applications/Music.app/PlugIns/RecentlyPlayedTodayExtension.appex/RecentlyPlayedTodayExtension
/System/Library/PrivateFrameworks/UpNextWidget.framework/PlugIns/UpNext.appex/UpNext

You will get these additional binaries from the dyld shared cache:

/System/Library/PrivateFrameworks/CoreKnowledge.framework/CoreKnowledge
/System/Library/PrivateFrameworks/Swift/libswiftAssetsLibrary.dylib
/System/Library/PrivateFrameworks/Swift/libswiftAVFoundation.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCloudKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftContacts.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCore.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreAudio.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreBluetooth.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreData.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreGraphics.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreImage.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreLocation.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreMedia.dylib
/System/Library/PrivateFrameworks/Swift/libswiftDarwin.dylib
/System/Library/PrivateFrameworks/Swift/libswiftDispatch.dylib
/System/Library/PrivateFrameworks/Swift/libswiftEventKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftFoundation.dylib
/System/Library/PrivateFrameworks/Swift/libswiftGameKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftGameplayKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftGLKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftHomeKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftLocalAuthentication.dylib
/System/Library/PrivateFrameworks/Swift/libswiftMultipeerConnectivity.dylib
/System/Library/PrivateFrameworks/Swift/libswiftObjectiveC.dylib
/System/Library/PrivateFrameworks/Swift/libswiftPassKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftRemoteMirror.dylib
/System/Library/PrivateFrameworks/Swift/libswiftSceneKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftsimd.dylib
/System/Library/PrivateFrameworks/Swift/libswiftSpriteKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftSwiftOnoneSupport.dylib
/System/Library/PrivateFrameworks/Swift/libswiftUIKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftWatchConnectivity.dylib
/System/Library/PrivateFrameworks/Swift/libswiftWatchKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftWebKit.dylib
/System/Library/PrivateFrameworks/UpNextWidget.framework/UpNextWidget

Note that you will get a similar output for an iPad except that the Calculator.app is not available.

Apple’s use of Swift in macOS 10.12.1

Running the script on macOS 10.12.1 will give you this list of binaries:

/Applications/Utilities/Console.app/Contents/MacOS/Console
/usr/bin/swift
/usr/bin/swiftc
/usr/sbin/usernoted
/System/Library/CoreServices/Dock.app/Contents/MacOS/Dock
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftAppKit.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftCore.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftCoreData.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftCoreGraphics.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftCoreImage.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftDarwin.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftDispatch.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftFoundation.dylib
/System/Library/CoreServices/MRT.app/Contents/Frameworks/libswiftObjectiveC.dylib
/System/Library/CoreServices/MRT.app/Contents/MacOS/MRT
/System/Library/CoreServices/NotificationCenter.app/Contents/MacOS/NotificationCenter
/System/Library/CoreServices/OSDUIHelper.app/Contents/MacOS/OSDUIHelper
/System/Library/CoreServices/PIPAgent.app/Contents/MacOS/PIPAgent
/System/Library/PrivateFrameworks/Swift/libswiftAppKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftAVFoundation.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCloudKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftContacts.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCore.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreAudio.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreBluetooth.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreData.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreGraphics.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreImage.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreLocation.dylib
/System/Library/PrivateFrameworks/Swift/libswiftCoreMedia.dylib
/System/Library/PrivateFrameworks/Swift/libswiftDarwin.dylib
/System/Library/PrivateFrameworks/Swift/libswiftDispatch.dylib
/System/Library/PrivateFrameworks/Swift/libswiftEventKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftFoundation.dylib
/System/Library/PrivateFrameworks/Swift/libswiftGameKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftGameplayKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftGLKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftIOKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftLocalAuthentication.dylib
/System/Library/PrivateFrameworks/Swift/libswiftMultipeerConnectivity.dylib
/System/Library/PrivateFrameworks/Swift/libswiftObjectiveC.dylib
/System/Library/PrivateFrameworks/Swift/libswiftOpenCL.dylib
/System/Library/PrivateFrameworks/Swift/libswiftRemoteMirror.dylib
/System/Library/PrivateFrameworks/Swift/libswiftSceneKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftsimd.dylib
/System/Library/PrivateFrameworks/Swift/libswiftSpriteKit.dylib
/System/Library/PrivateFrameworks/Swift/libswiftSwiftOnoneSupport.dylib
/System/Library/PrivateFrameworks/Swift/libswiftWebKit.dylib

Note that you will get a lot of matches in Xcode 8.1. If you exclude the various toolchains and platform SDKs, you will get:

/Applications/Xcode.app/Contents/Frameworks/IDEDocumentation.framework/Versions/A/IDEDocumentation
/Applications/Xcode.app/Contents/Frameworks/libswiftAppKit.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftAVFoundation.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftCore.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftCoreAudio.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftCoreData.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftCoreGraphics.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftCoreImage.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftCoreMedia.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftDarwin.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftDispatch.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftFoundation.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftIOKit.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftObjectiveC.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftQuartzCore.dylib
/Applications/Xcode.app/Contents/Frameworks/libswiftXPC.dylib
/Applications/Xcode.app/Contents/PlugIns/IDEDocViewer.ideplugin/Contents/MacOS/IDEDocViewer
/Applications/Xcode.app/Contents/PlugIns/IDELanguageSupportUI.ideplugin/Contents/MacOS/IDELanguageSupportUI
/Applications/Xcode.app/Contents/PlugIns/IDEQuickHelp.ideplugin/Contents/MacOS/IDEQuickHelp
/Applications/Xcode.app/Contents/PlugIns/XcodeBuiltInExtensions.appex/Contents/MacOS/XcodeBuiltInExtensions
/Applications/Xcode.app/Contents/SharedFrameworks/DNTDocumentationModel.framework/Versions/A/DNTDocumentationModel
/Applications/Xcode.app/Contents/SharedFrameworks/DNTDocumentationSupport.framework/Versions/A/DNTDocumentationSupport
/Applications/Xcode.app/Contents/SharedFrameworks/DNTSourceKitSupport.framework/Versions/A/DNTSourceKitSupport
/Applications/Xcode.app/Contents/SharedFrameworks/DNTTransformer.framework/Versions/A/DNTTransformer
/Applications/Xcode.app/Contents/SharedFrameworks/DVTDocumentation.framework/Versions/A/DVTDocumentation
/Applications/Xcode.app/Contents/SharedFrameworks/DVTMarkup.framework/Versions/A/DVTMarkup
/Applications/Xcode.app/Contents/SharedFrameworks/LLDB.framework/Versions/A/Resources/repl_swift
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftCore.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftCoreGraphics.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftDarwin.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftDispatch.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftFoundation.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftIOKit.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/Frameworks/libswiftObjectiveC.dylib
/Applications/Xcode.app/Contents/SharedFrameworks/SourceKit.framework/Versions/A/SourceKit

Conclusion

Apple’s use of Swift in iOS 10.1 and macOS 10.12.1 is extremely limited.
On iOS 10.1 there are only 2 apps and 2 private frameworks using Swift:

  • Calculator.app (iPhone only)
  • Music.app
  • UpNextWidget.framework
  • CoreKnowledge.framework

On macOS 10.12.1 the list of apps using Swift is limited to:

  • Console
  • swift
  • swiftc
  • usernoted
  • Dock.app
  • MRT.app
  • NotificationCenter.app
  • OSDUIHelper.app
  • PIPAgent.app
  • (Xcode.app)