[Mini-proposal] Require @nonobjc on members of @objc protocol extensions

Charles_Srstka · January 6, 2016, 9:55pm

Okay, here’s a more serious, less devil’s-advocatey sketch. It would require one tweak to the compiler to allow the swiftImplementationForSelector() method to be vtable dispatched. Otherwise, it pretty much works:

The basic protocol:

@objc protocol HasSwiftExtension {}

extension HasSwiftExtension {
    // Problem: This method won't correctly be dispatched, and instead this implementation will always be called.
    // The method cannot be declared in the protocol, because then Swift would try to use the Objective-C runtime
    // to find it (and fail). Some way to declare methods in extensions that are dispatched via the vtable would
    // need to be added for this to work properly.
    func swiftImplementationForSelector(selector: Selector) -> (implementation: IMP, types: String)? {
        return nil
    }
}

extension NSObject {
    class func somePrefixHere_SwizzledResolveInstanceMethod(selector: Selector) -> Bool {
        // Doesn't work as written because of the lack of vtable dispatch.
        // However, if you change "as? HasSwiftExtension" to "as? P" below, it will work in the case of P.
        if let swiftySelf = self as? HasSwiftExtension {
            // Yes, here we are calling an instance method from a class object.
            // It works because the NSObject class is technically also an instance of NSObject.
            // It would be better to use a class method, but Swift doesn't allow declaring those
            // in protocols or extensions.
            if let (implementation: imp, types: types) = swiftySelf.swiftImplementationForSelector(selector) {
                class_addMethod(self, selector, imp, types)
                return true
            }
        }

        return somePrefixHere_SwizzledResolveInstanceMethod(selector)
    }
}

The Objective-C shim to do the swizzling:

@interface NSObject(Swizzle)
@end

@implementation NSObject(Swizzle)

+ (void)load {
    Method m1 = class_getClassMethod(self, @selector(resolveInstanceMethod:));
    Method m2 = class_getClassMethod(self, @selector(somePrefixHere_SwizzledResolveInstanceMethod:));

    method_exchangeImplementations(m1, m2);
}

@end

Sample protocol and class conforming to this:

// HasSwiftExtension conformance would be added automatically by the compiler.
@objc protocol P: HasSwiftExtension {
optional func foo() // optional only to avoid that compiler crash
}

class C: NSObject, P {}

extension P {
    // This method would be added automatically by the compiler.
    func swiftImplementationForSelector(selector: Selector) -> (implementation: IMP, types: String)? {
        switch selector {
        case "foo":
            let block: @convention(block) (P) -> () = { $0.foo() }
            let imp = imp_implementationWithBlock(unsafeBitCast(block, AnyObject.self))

            return (implementation: imp, types: "v@:")
        default:
            return nil
        }
    }

    func foo() { print("foo was called") }
}

Changing “as? HasSwiftExtension” to “as? P” in somePrefixHere_SwizzledResolveInstanceMethod(), and then calling this in main:

let c = C()

c.performSelector("foo")

outputs:

foo was called
Program ended with exit code: 0

I think it could be doable.

Charles

···

On Jan 5, 2016, at 8:55 PM, Charles Srstka via swift-evolution <swift-evolution@swift.org> wrote:

On Jan 5, 2016, at 8:29 PM, Greg Parker <gparker@apple.com <mailto:gparker@apple.com>> wrote:

On Jan 5, 2016, at 3:37 PM, Charles Srstka via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Jan 5, 2016, at 11:52 AM, Douglas Gregor <dgregor@apple.com <mailto:dgregor@apple.com>> wrote:

There are better mechanisms for this than +load. But one would have to deal with the dylib loading issue and the need to enumerate root classes to get to a complete implementation. Frankly, I don’t think this level of Objective-C runtime hackery is worth the effort, hence my suggestion to make the existing behavior explicit.

Yeah, +load was just to throw together a quick-and-dirty demonstration, and not what you’d actually use. You have a point about libraries and bundles; you’d have to hook into that and rescan each time new code was dynamically loaded. However, the enumeration of classes only seems to take around 0.001 seconds, so I don’t think it’s terrible.

Enumeration of classes is terrible: it forces the runtime to perform lots of work that it tries very hard to perform lazily otherwise. I would expect your measured cost to be much higher if you had linked to more high-level libraries (UIKit, MapKit, etc).

That was my gut reaction to the idea also, when I had it, but it seems to run pretty fast no matter what I do. I just tried dragging every framework from /System/Library/Frameworks into the project, removing only the Java frameworks, Kernel.framework, Message.framework, and vecLib.framework. Time taken was 0.004260 seconds.

It is, of course, ugly and hacky as hell, and that might make a pretty good reason not to do it. :-/ What do you think about the other idea, of adding to NSObject’s default implementation of +resolveInstanceMethod:? That *would* be done lazily, and would avoid all the problems involving dynamically loaded code.

Charles_Srstka · January 6, 2016, 3:19am

objc_copyClassList leaves a value of 14694 in classCount. When I just link against Foundation it only gives 1581.

otool says:

$ otool -L test
test:
  /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.1.0)
  /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 1256.1.0)
  /System/Library/Frameworks/CFNetwork.framework/Versions/A/CFNetwork (compatibility version 1.0.0, current version 760.2.5)
  /System/Library/Frameworks/Metal.framework/Versions/A/Metal (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Contacts.framework/Versions/A/Contacts (compatibility version 0.0.0, current version 0.0.0)
  /System/Library/Frameworks/GSS.framework/Versions/A/GSS (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreMIDIServer.framework/Versions/A/CoreMIDIServer (compatibility version 1.0.0, current version 73.0.0)
  /System/Library/Frameworks/Python.framework/Versions/2.7/Python (compatibility version 2.7.0, current version 2.7.10)
  /System/Library/Frameworks/CoreLocation.framework/Versions/A/CoreLocation (compatibility version 1.0.0, current version 1615.38.0)
  /System/Library/Frameworks/GLKit.framework/Versions/A/GLKit (compatibility version 1.0.0, current version 20.0.0)
  /System/Library/Frameworks/MapKit.framework/Versions/A/MapKit (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/ServiceManagement.framework/Versions/A/ServiceManagement (compatibility version 1.0.0, current version 756.20.4)
  /System/Library/Frameworks/CoreTelephony.framework/Versions/A/CoreTelephony (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/CloudKit.framework/Versions/A/CloudKit (compatibility version 1.0.0, current version 481.8.0)
  /System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreText.framework/Versions/A/CoreText (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Collaboration.framework/Versions/A/Collaboration (compatibility version 1.0.0, current version 75.0.0)
  /System/Library/Frameworks/LDAP.framework/Versions/A/LDAP (compatibility version 1.0.0, current version 2.4.0)
  /System/Library/Frameworks/AddressBook.framework/Versions/A/AddressBook (compatibility version 1.0.0, current version 1679.3.0)
  /System/Library/Frameworks/QuickLook.framework/Versions/A/QuickLook (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/DiskArbitration.framework/Versions/A/DiskArbitration (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Tcl.framework/Versions/8.5/Tcl (compatibility version 8.5.0, current version 8.5.9)
  /System/Library/Frameworks/DiscRecording.framework/Versions/A/DiscRecording (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/InputMethodKit.framework/Versions/A/InputMethodKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/OpenCL.framework/Versions/A/OpenCL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Photos.framework/Versions/A/Photos (compatibility version 1.0.0, current version 350.22.0)
  /System/Library/Frameworks/OSAKit.framework/Versions/A/OSAKit (compatibility version 1.0.0, current version 104.0.0)
  /System/Library/Frameworks/MediaAccessibility.framework/Versions/A/MediaAccessibility (compatibility version 1.0.0, current version 62.0.0)
  /System/Library/Frameworks/ContactsUI.framework/Versions/A/ContactsUI (compatibility version 1.0.0, current version 1679.3.0)
  /System/Library/Frameworks/DirectoryService.framework/Versions/A/DirectoryService (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/AGL.framework/Versions/A/AGL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/StoreKit.framework/Versions/A/StoreKit (compatibility version 1.0.0, current version 379.0.0)
  /System/Library/Frameworks/OpenDirectory.framework/Versions/A/OpenDirectory (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/PreferencePanes.framework/Versions/A/PreferencePanes (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GameplayKit.framework/Versions/A/GameplayKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SyncServices.framework/Versions/A/SyncServices (compatibility version 48.0.0, current version 724.0.0)
  /System/Library/Frameworks/AVKit.framework/Versions/A/AVKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GLUT.framework/Versions/A/GLUT (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ModelIO.framework/Versions/A/ModelIO (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GameController.framework/Versions/A/GameController (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Tk.framework/Versions/8.5/Tk (compatibility version 8.5.0, current version 8.5.9)
  /System/Library/Frameworks/AppleScriptObjC.framework/Versions/A/AppleScriptObjC (compatibility version 1.0.0, current version 32.0.0)
  /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit (compatibility version 45.0.0, current version 1404.32.0)
  /System/Library/Frameworks/InstallerPlugins.framework/Versions/A/InstallerPlugins (compatibility version 1.0.0, current version 815.0.0)
  /System/Library/Frameworks/SecurityFoundation.framework/Versions/A/SecurityFoundation (compatibility version 1.0.0, current version 55126.0.0)
  /System/Library/Frameworks/ImageCaptureCore.framework/Versions/A/ImageCaptureCore (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/VideoDecodeAcceleration.framework/Versions/A/VideoDecodeAcceleration (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreGraphics.framework/Versions/A/CoreGraphics (compatibility version 64.0.0, current version 600.0.0)
  /System/Library/Frameworks/Kerberos.framework/Versions/A/Kerberos (compatibility version 5.0.0, current version 6.0.0)
  /System/Library/Frameworks/vmnet.framework/Versions/A/vmnet (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Quartz.framework/Versions/A/Quartz (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreData.framework/Versions/A/CoreData (compatibility version 1.0.0, current version 641.3.0)
  /System/Library/Frameworks/IMServicePlugIn.framework/Versions/A/IMServicePlugIn (compatibility version 1.0.0, current version 1000.0.0)
  /System/Library/Frameworks/JavaScriptCore.framework/Versions/A/JavaScriptCore (compatibility version 1.0.0, current version 601.3.7)
  /System/Library/Frameworks/NotificationCenter.framework/Versions/A/NotificationCenter (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/LocalAuthentication.framework/Versions/A/LocalAuthentication (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GameKit.framework/Versions/A/GameKit (compatibility version 1.0.0, current version 365.103.0)
  /System/Library/Frameworks/PubSub.framework/Versions/A/PubSub (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreMediaIO.framework/Versions/A/CoreMediaIO (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Social.framework/Versions/A/Social (compatibility version 1.0.0, current version 538.0.0)
  /System/Library/Frameworks/MultipeerConnectivity.framework/Versions/A/MultipeerConnectivity (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreVideo.framework/Versions/A/CoreVideo (compatibility version 1.2.0, current version 1.5.0)
  /System/Library/Frameworks/IOKit.framework/Versions/A/IOKit (compatibility version 1.0.0, current version 275.0.0)
  /System/Library/Frameworks/QTKit.framework/Versions/A/QTKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ApplicationServices.framework/Versions/A/ApplicationServices (compatibility version 1.0.0, current version 48.0.0)
  /System/Library/Frameworks/NetworkExtension.framework/Versions/A/NetworkExtension (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/PCSC.framework/Versions/A/PCSC (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ExceptionHandling.framework/Versions/A/ExceptionHandling (compatibility version 1.0.0, current version 11.0.0)
  /System/Library/Frameworks/Carbon.framework/Versions/A/Carbon (compatibility version 2.0.0, current version 157.0.0)
  /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57337.20.43)
  /System/Library/Frameworks/AppleScriptKit.framework/Versions/A/AppleScriptKit (compatibility version 1.0.0, current version 83.0.0)
  /System/Library/Frameworks/LatentSemanticMapping.framework/Versions/A/LatentSemanticMapping (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/libruby.2.0.0.dylib (compatibility version 2.0.0, current version 2.0.0)
  /System/Library/Frameworks/InstantMessage.framework/Versions/A/InstantMessage (compatibility version 1.0.0, current version 800.0.0)
  /System/Library/Frameworks/AudioVideoBridging.framework/Versions/A/AudioVideoBridging (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreImage.framework/Versions/A/CoreImage (compatibility version 1.0.1, current version 2.0.0)
  /System/Library/Frameworks/Automator.framework/Versions/A/Automator (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/MetalKit.framework/Versions/A/MetalKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Hypervisor.framework/Versions/A/Hypervisor (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SceneKit.framework/Versions/A/SceneKit (compatibility version 1.0.0, current version 186.0.0)
  /System/Library/Frameworks/OpenAL.framework/Versions/A/OpenAL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/EventKit.framework/Versions/A/EventKit (compatibility version 1.0.0, current version 487.3.0)
  /System/Library/Frameworks/CoreBluetooth.framework/Versions/A/CoreBluetooth (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/IOBluetoothUI.framework/Versions/A/IOBluetoothUI (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CalendarStore.framework/Versions/A/CalendarStore (compatibility version 1.0.0, current version 1501.0.0)
  /System/Library/Frameworks/SpriteKit.framework/Versions/A/SpriteKit (compatibility version 1.0.0, current version 2.0.0)
  /System/Library/Frameworks/VideoToolbox.framework/Versions/A/VideoToolbox (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/AudioToolbox.framework/Versions/A/AudioToolbox (compatibility version 1.0.0, current version 492.0.0)
  /System/Library/Frameworks/ForceFeedback.framework/Versions/A/ForceFeedback (compatibility version 1.0.0, current version 1.0.2)
  /System/Library/Frameworks/NetFS.framework/Versions/A/NetFS (compatibility version 1.0.0, current version 1.0.0)
  @rpath/FinderSync.framework/Versions/A/FinderSync (compatibility version 1.0.0, current version 960.2.6)
  /System/Library/Frameworks/WebKit.framework/Versions/A/WebKit (compatibility version 1.0.0, current version 601.3.9)
  /System/Library/Frameworks/TWAIN.framework/Versions/A/TWAIN (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreAudio.framework/Versions/A/CoreAudio (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SecurityInterface.framework/Versions/A/SecurityInterface (compatibility version 1.0.0, current version 55065.20.1)
  /System/Library/Frameworks/CoreMedia.framework/Versions/A/CoreMedia (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreMIDI.framework/Versions/A/CoreMIDI (compatibility version 1.0.0, current version 73.0.0)
  /System/Library/Frameworks/ICADevices.framework/Versions/A/ICADevices (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/MediaToolbox.framework/Versions/A/MediaToolbox (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreAudioKit.framework/Versions/A/CoreAudioKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Accounts.framework/Versions/A/Accounts (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/PhotosUI.framework/Versions/A/PhotosUI (compatibility version 1.0.0, current version 350.22.0)
  /System/Library/Frameworks/DVDPlayback.framework/Versions/A/DVDPlayback (compatibility version 5000.0.0, current version 5950.0.0)
  /System/Library/Frameworks/DiscRecordingUI.framework/Versions/A/DiscRecordingUI (compatibility version 1.0.0, current version 1.0.0)
  /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)
  /System/Library/Frameworks/ScriptingBridge.framework/Versions/A/ScriptingBridge (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreWLAN.framework/Versions/A/CoreWLAN (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CryptoTokenKit.framework/Versions/A/CryptoTokenKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ScreenSaver.framework/Versions/A/ScreenSaver (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Cocoa.framework/Versions/A/Cocoa (compatibility version 1.0.0, current version 22.0.0)
  /System/Library/Frameworks/QuartzCore.framework/Versions/A/QuartzCore (compatibility version 1.2.0, current version 1.11.0)
  /System/Library/Frameworks/OpenGL.framework/Versions/A/OpenGL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreServices.framework/Versions/A/CoreServices (compatibility version 1.0.0, current version 728.6.0)
  /System/Library/Frameworks/MediaLibrary.framework/Versions/A/MediaLibrary (compatibility version 1.0.0, current version 721.0.0)
  /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1256.14.0)
  /System/Library/Frameworks/Accelerate.framework/Versions/A/Accelerate (compatibility version 1.0.0, current version 4.0.0)
  /System/Library/Frameworks/AVFoundation.framework/Versions/A/AVFoundation (compatibility version 1.0.0, current version 2.0.0)
  /System/Library/Frameworks/FWAUserLib.framework/Versions/A/FWAUserLib (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/AudioUnit.framework/Versions/A/AudioUnit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/IOSurface.framework/Versions/A/IOSurface (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SystemConfiguration.framework/Versions/A/SystemConfiguration (compatibility version 1.0.0, current version 802.20.7)
  /System/Library/Frameworks/IOBluetooth.framework/Versions/A/IOBluetooth (compatibility version 1.0.0, current version 1.0.0)
  /usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)

I don't think the optimization you describe is possible with Objective-C due to the dynamic nature of the runtime. The linker has no way of knowing that a class won’t be accessed via NSClassFromString(), or from a nib file or something.

Charles

···

On Jan 5, 2016, at 9:06 PM, Félix Cloutier <felixcca@yahoo.ca> wrote:

The linker is smart enough to get rid of frameworks that you don't actually use.

Félix

Felix_Cloutier1 · January 6, 2016, 3:20am

I stand corrected.

Félix

···

Le 5 janv. 2016 à 22:19:28, Charles Srstka <cocoadev@charlessoft.com> a écrit :

On Jan 5, 2016, at 9:06 PM, Félix Cloutier <felixcca@yahoo.ca <mailto:felixcca@yahoo.ca>> wrote:

The linker is smart enough to get rid of frameworks that you don't actually use.

Félix

objc_copyClassList leaves a value of 14694 in classCount. When I just link against Foundation it only gives 1581.

otool says:

$ otool -L test
test:
  /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.1.0)
  /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 1256.1.0)
  /System/Library/Frameworks/CFNetwork.framework/Versions/A/CFNetwork (compatibility version 1.0.0, current version 760.2.5)
  /System/Library/Frameworks/Metal.framework/Versions/A/Metal (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Contacts.framework/Versions/A/Contacts (compatibility version 0.0.0, current version 0.0.0)
  /System/Library/Frameworks/GSS.framework/Versions/A/GSS (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreMIDIServer.framework/Versions/A/CoreMIDIServer (compatibility version 1.0.0, current version 73.0.0)
  /System/Library/Frameworks/Python.framework/Versions/2.7/Python (compatibility version 2.7.0, current version 2.7.10)
  /System/Library/Frameworks/CoreLocation.framework/Versions/A/CoreLocation (compatibility version 1.0.0, current version 1615.38.0)
  /System/Library/Frameworks/GLKit.framework/Versions/A/GLKit (compatibility version 1.0.0, current version 20.0.0)
  /System/Library/Frameworks/MapKit.framework/Versions/A/MapKit (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/ServiceManagement.framework/Versions/A/ServiceManagement (compatibility version 1.0.0, current version 756.20.4)
  /System/Library/Frameworks/CoreTelephony.framework/Versions/A/CoreTelephony (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/CloudKit.framework/Versions/A/CloudKit (compatibility version 1.0.0, current version 481.8.0)
  /System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreText.framework/Versions/A/CoreText (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Collaboration.framework/Versions/A/Collaboration (compatibility version 1.0.0, current version 75.0.0)
  /System/Library/Frameworks/LDAP.framework/Versions/A/LDAP (compatibility version 1.0.0, current version 2.4.0)
  /System/Library/Frameworks/AddressBook.framework/Versions/A/AddressBook (compatibility version 1.0.0, current version 1679.3.0)
  /System/Library/Frameworks/QuickLook.framework/Versions/A/QuickLook (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/DiskArbitration.framework/Versions/A/DiskArbitration (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Tcl.framework/Versions/8.5/Tcl (compatibility version 8.5.0, current version 8.5.9)
  /System/Library/Frameworks/DiscRecording.framework/Versions/A/DiscRecording (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/InputMethodKit.framework/Versions/A/InputMethodKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/OpenCL.framework/Versions/A/OpenCL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Photos.framework/Versions/A/Photos (compatibility version 1.0.0, current version 350.22.0)
  /System/Library/Frameworks/OSAKit.framework/Versions/A/OSAKit (compatibility version 1.0.0, current version 104.0.0)
  /System/Library/Frameworks/MediaAccessibility.framework/Versions/A/MediaAccessibility (compatibility version 1.0.0, current version 62.0.0)
  /System/Library/Frameworks/ContactsUI.framework/Versions/A/ContactsUI (compatibility version 1.0.0, current version 1679.3.0)
  /System/Library/Frameworks/DirectoryService.framework/Versions/A/DirectoryService (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/AGL.framework/Versions/A/AGL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/StoreKit.framework/Versions/A/StoreKit (compatibility version 1.0.0, current version 379.0.0)
  /System/Library/Frameworks/OpenDirectory.framework/Versions/A/OpenDirectory (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/PreferencePanes.framework/Versions/A/PreferencePanes (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GameplayKit.framework/Versions/A/GameplayKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SyncServices.framework/Versions/A/SyncServices (compatibility version 48.0.0, current version 724.0.0)
  /System/Library/Frameworks/AVKit.framework/Versions/A/AVKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GLUT.framework/Versions/A/GLUT (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ModelIO.framework/Versions/A/ModelIO (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GameController.framework/Versions/A/GameController (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Tk.framework/Versions/8.5/Tk (compatibility version 8.5.0, current version 8.5.9)
  /System/Library/Frameworks/AppleScriptObjC.framework/Versions/A/AppleScriptObjC (compatibility version 1.0.0, current version 32.0.0)
  /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit (compatibility version 45.0.0, current version 1404.32.0)
  /System/Library/Frameworks/InstallerPlugins.framework/Versions/A/InstallerPlugins (compatibility version 1.0.0, current version 815.0.0)
  /System/Library/Frameworks/SecurityFoundation.framework/Versions/A/SecurityFoundation (compatibility version 1.0.0, current version 55126.0.0)
  /System/Library/Frameworks/ImageCaptureCore.framework/Versions/A/ImageCaptureCore (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/VideoDecodeAcceleration.framework/Versions/A/VideoDecodeAcceleration (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreGraphics.framework/Versions/A/CoreGraphics (compatibility version 64.0.0, current version 600.0.0)
  /System/Library/Frameworks/Kerberos.framework/Versions/A/Kerberos (compatibility version 5.0.0, current version 6.0.0)
  /System/Library/Frameworks/vmnet.framework/Versions/A/vmnet (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Quartz.framework/Versions/A/Quartz (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreData.framework/Versions/A/CoreData (compatibility version 1.0.0, current version 641.3.0)
  /System/Library/Frameworks/IMServicePlugIn.framework/Versions/A/IMServicePlugIn (compatibility version 1.0.0, current version 1000.0.0)
  /System/Library/Frameworks/JavaScriptCore.framework/Versions/A/JavaScriptCore (compatibility version 1.0.0, current version 601.3.7)
  /System/Library/Frameworks/NotificationCenter.framework/Versions/A/NotificationCenter (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/LocalAuthentication.framework/Versions/A/LocalAuthentication (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/GameKit.framework/Versions/A/GameKit (compatibility version 1.0.0, current version 365.103.0)
  /System/Library/Frameworks/PubSub.framework/Versions/A/PubSub (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreMediaIO.framework/Versions/A/CoreMediaIO (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Social.framework/Versions/A/Social (compatibility version 1.0.0, current version 538.0.0)
  /System/Library/Frameworks/MultipeerConnectivity.framework/Versions/A/MultipeerConnectivity (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreVideo.framework/Versions/A/CoreVideo (compatibility version 1.2.0, current version 1.5.0)
  /System/Library/Frameworks/IOKit.framework/Versions/A/IOKit (compatibility version 1.0.0, current version 275.0.0)
  /System/Library/Frameworks/QTKit.framework/Versions/A/QTKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ApplicationServices.framework/Versions/A/ApplicationServices (compatibility version 1.0.0, current version 48.0.0)
  /System/Library/Frameworks/NetworkExtension.framework/Versions/A/NetworkExtension (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/PCSC.framework/Versions/A/PCSC (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ExceptionHandling.framework/Versions/A/ExceptionHandling (compatibility version 1.0.0, current version 11.0.0)
  /System/Library/Frameworks/Carbon.framework/Versions/A/Carbon (compatibility version 2.0.0, current version 157.0.0)
  /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57337.20.43)
  /System/Library/Frameworks/AppleScriptKit.framework/Versions/A/AppleScriptKit (compatibility version 1.0.0, current version 83.0.0)
  /System/Library/Frameworks/LatentSemanticMapping.framework/Versions/A/LatentSemanticMapping (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/libruby.2.0.0.dylib (compatibility version 2.0.0, current version 2.0.0)
  /System/Library/Frameworks/InstantMessage.framework/Versions/A/InstantMessage (compatibility version 1.0.0, current version 800.0.0)
  /System/Library/Frameworks/AudioVideoBridging.framework/Versions/A/AudioVideoBridging (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreImage.framework/Versions/A/CoreImage (compatibility version 1.0.1, current version 2.0.0)
  /System/Library/Frameworks/Automator.framework/Versions/A/Automator (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/MetalKit.framework/Versions/A/MetalKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Hypervisor.framework/Versions/A/Hypervisor (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SceneKit.framework/Versions/A/SceneKit (compatibility version 1.0.0, current version 186.0.0)
  /System/Library/Frameworks/OpenAL.framework/Versions/A/OpenAL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/EventKit.framework/Versions/A/EventKit (compatibility version 1.0.0, current version 487.3.0)
  /System/Library/Frameworks/CoreBluetooth.framework/Versions/A/CoreBluetooth (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/IOBluetoothUI.framework/Versions/A/IOBluetoothUI (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CalendarStore.framework/Versions/A/CalendarStore (compatibility version 1.0.0, current version 1501.0.0)
  /System/Library/Frameworks/SpriteKit.framework/Versions/A/SpriteKit (compatibility version 1.0.0, current version 2.0.0)
  /System/Library/Frameworks/VideoToolbox.framework/Versions/A/VideoToolbox (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/AudioToolbox.framework/Versions/A/AudioToolbox (compatibility version 1.0.0, current version 492.0.0)
  /System/Library/Frameworks/ForceFeedback.framework/Versions/A/ForceFeedback (compatibility version 1.0.0, current version 1.0.2)
  /System/Library/Frameworks/NetFS.framework/Versions/A/NetFS (compatibility version 1.0.0, current version 1.0.0)
  @rpath/FinderSync.framework/Versions/A/FinderSync (compatibility version 1.0.0, current version 960.2.6)
  /System/Library/Frameworks/WebKit.framework/Versions/A/WebKit (compatibility version 1.0.0, current version 601.3.9)
  /System/Library/Frameworks/TWAIN.framework/Versions/A/TWAIN (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreAudio.framework/Versions/A/CoreAudio (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SecurityInterface.framework/Versions/A/SecurityInterface (compatibility version 1.0.0, current version 55065.20.1)
  /System/Library/Frameworks/CoreMedia.framework/Versions/A/CoreMedia (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreMIDI.framework/Versions/A/CoreMIDI (compatibility version 1.0.0, current version 73.0.0)
  /System/Library/Frameworks/ICADevices.framework/Versions/A/ICADevices (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/MediaToolbox.framework/Versions/A/MediaToolbox (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreAudioKit.framework/Versions/A/CoreAudioKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Accounts.framework/Versions/A/Accounts (compatibility version 1.0.0, current version 0.0.0)
  /System/Library/Frameworks/PhotosUI.framework/Versions/A/PhotosUI (compatibility version 1.0.0, current version 350.22.0)
  /System/Library/Frameworks/DVDPlayback.framework/Versions/A/DVDPlayback (compatibility version 5000.0.0, current version 5950.0.0)
  /System/Library/Frameworks/DiscRecordingUI.framework/Versions/A/DiscRecordingUI (compatibility version 1.0.0, current version 1.0.0)
  /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)
  /System/Library/Frameworks/ScriptingBridge.framework/Versions/A/ScriptingBridge (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreWLAN.framework/Versions/A/CoreWLAN (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CryptoTokenKit.framework/Versions/A/CryptoTokenKit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/ScreenSaver.framework/Versions/A/ScreenSaver (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/Cocoa.framework/Versions/A/Cocoa (compatibility version 1.0.0, current version 22.0.0)
  /System/Library/Frameworks/QuartzCore.framework/Versions/A/QuartzCore (compatibility version 1.2.0, current version 1.11.0)
  /System/Library/Frameworks/OpenGL.framework/Versions/A/OpenGL (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/CoreServices.framework/Versions/A/CoreServices (compatibility version 1.0.0, current version 728.6.0)
  /System/Library/Frameworks/MediaLibrary.framework/Versions/A/MediaLibrary (compatibility version 1.0.0, current version 721.0.0)
  /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1256.14.0)
  /System/Library/Frameworks/Accelerate.framework/Versions/A/Accelerate (compatibility version 1.0.0, current version 4.0.0)
  /System/Library/Frameworks/AVFoundation.framework/Versions/A/AVFoundation (compatibility version 1.0.0, current version 2.0.0)
  /System/Library/Frameworks/FWAUserLib.framework/Versions/A/FWAUserLib (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/AudioUnit.framework/Versions/A/AudioUnit (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/IOSurface.framework/Versions/A/IOSurface (compatibility version 1.0.0, current version 1.0.0)
  /System/Library/Frameworks/SystemConfiguration.framework/Versions/A/SystemConfiguration (compatibility version 1.0.0, current version 802.20.7)
  /System/Library/Frameworks/IOBluetooth.framework/Versions/A/IOBluetooth (compatibility version 1.0.0, current version 1.0.0)
  /usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)

I don't think the optimization you describe is possible with Objective-C due to the dynamic nature of the runtime. The linker has no way of knowing that a class won’t be accessed via NSClassFromString(), or from a nib file or something.

Charles