My improvements:

Use synthesized properties for CSMissingROM.
Remove openGLView from the xib: that will quiet a warning.
Add nullability metadata to CSStaticAnalyser.

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -1332,7 +1332,6 @@
 		4B9378E322A199C600973513 /* Audio.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Audio.hpp; sourceTree = "<group>"; };
 		4B95FA9C1F11893B0008E395 /* ZX8081OptionsPanel.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ZX8081OptionsPanel.swift; sourceTree = "<group>"; };
 		4B961408222760E0001A7BF2 /* Screenshot.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Screenshot.hpp; sourceTree = "<group>"; };
-		4B97ADC722C6FD9B00A22A41 /* 68000ArithmeticTests.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; name = 68000ArithmeticTests.mm; path = "/Users/thomasharte/Projects/CLK/OSBindings/Mac/Clock SignalTests/68000ArithmeticTests.mm"; sourceTree = "<absolute>"; };
 		4B98A05C1FFAD3F600ADF63B /* CSROMFetcher.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = CSROMFetcher.hpp; sourceTree = "<group>"; };
 		4B98A05D1FFAD3F600ADF63B /* CSROMFetcher.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = CSROMFetcher.mm; sourceTree = "<group>"; };
 		4B98A0601FFADCDE00ADF63B /* MSXStaticAnalyserTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MSXStaticAnalyserTests.mm; sourceTree = "<group>"; };
@@ -3442,7 +3441,7 @@
 			children = (
 				4B85322922778E4200F26553 /* Comparative68000.hpp */,
 				4B90467222C6FA31000E2074 /* TestRunner68000.hpp */,
-				4B97ADC722C6FD9B00A22A41 /* 68000ArithmeticTests.mm */,
+				4B90467522C6FD6E000E2074 /* 68000ArithmeticTests.mm */,
 				4B9D0C4A22C7D70900DE1AD3 /* 68000BCDTests.mm */,
 				4B90467322C6FADD000E2074 /* 68000BitwiseTests.mm */,
 				4B680CE123A5553100451D43 /* 68000ComparativeTests.mm */,
@@ -3485,7 +3484,6 @@
 				4BFCA12A1ECBE7C400AC40C1 /* ZexallTests.swift */,
 				4B3BA0C41D318B44005DD7A7 /* Bridges */,
 				4B1414631B588A1100E04248 /* Test Binaries */,
-				4B90467522C6FD6E000E2074 /* 68000ArithmeticTests.mm */,
 			);
 			path = "Clock SignalTests";
 			sourceTree = "<group>";

OSBindings/Mac/Clock Signal/Base.lproj/MachineDocument.xib

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="16097.2" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="15705" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
     <dependencies>
         <deployment identifier="macosx"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="16097.2"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="15705"/>
         <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
     </dependencies>
     <objects>
@@ -21,15 +21,15 @@
             <windowCollectionBehavior key="collectionBehavior" fullScreenPrimary="YES"/>
             <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
             <rect key="contentRect" x="80" y="250" width="600" height="450"/>
-            <rect key="screenRect" x="0.0" y="0.0" width="3840" height="2137"/>
+            <rect key="screenRect" x="0.0" y="0.0" width="1440" height="877"/>
             <value key="minSize" type="size" width="228" height="171"/>
             <view key="contentView" id="gIp-Ho-8D9">
                 <rect key="frame" x="0.0" y="0.0" width="600" height="450"/>
                 <autoresizingMask key="autoresizingMask"/>
                 <subviews>
-                    <openGLView hidden="YES" wantsLayer="YES" useAuxiliaryDepthBufferStencil="NO" allowOffline="YES" wantsBestResolutionOpenGLSurface="YES" translatesAutoresizingMaskIntoConstraints="NO" id="DEG-fq-cjd" customClass="CSScanTargetView">
+                    <view hidden="YES" wantsLayer="YES" translatesAutoresizingMaskIntoConstraints="NO" id="DEG-fq-cjd" customClass="CSScanTargetView">
                         <rect key="frame" x="0.0" y="0.0" width="600" height="450"/>
-                    </openGLView>
+                    </view>
                     <box hidden="YES" boxType="custom" cornerRadius="4" title="Box" titlePosition="noTitle" translatesAutoresizingMaskIntoConstraints="NO" id="4ap-Gi-2AO">
                         <rect key="frame" x="150" y="20" width="300" height="48"/>
                         <view key="contentView" id="gwO-Ty-LCX">

OSBindings/Mac/Clock Signal/CSApplication.h

@@ -13,7 +13,7 @@
 
 @class CSApplication;
 
-@protocol CSApplicationEventDelegate
+@protocol CSApplicationEventDelegate <NSObject>
 - (BOOL)application:(nonnull CSApplication *)application shouldSendEvent:(nonnull NSEvent *)event;
 @end
 

OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift

@@ -95,7 +95,7 @@ class MachineDocument:
 		//
 		// So: MAKE SURE IT'S SAFE TO ENTER THIS FUNCTION TWICE. Hence the non-assumption here about
 		// any windows still existing.
-		if self.windowControllers.count > 0, let window = self.windowControllers[0].window {
+		if let window = self.windowControllers.first?.window {
 			for sheet in window.sheets {
 				window.endSheet(sheet)
 			}
@@ -146,10 +146,7 @@ class MachineDocument:
 		} else {
 			// Store the selected machine and list of missing ROMs, and
 			// show the missing ROMs dialogue.
-			self.missingROMs = []
-			for untypedMissingROM in missingROMs {
-				self.missingROMs.append(untypedMissingROM as! CSMissingROM)
-			}
+			self.missingROMs = missingROMs.map({$0 as! CSMissingROM})
 
 			requestRoms()
 		}
@@ -252,7 +249,7 @@ class MachineDocument:
 		// TODO: this needs to be threadsafe. FIX!
 		let maximumSamplingRate = CSAudioQueue.preferredSamplingRate()
 		let selectedSamplingRate = Float64(self.machine.idealSamplingRate(from: NSRange(location: 0, length: NSInteger(maximumSamplingRate))))
-		let isStereo = self.machine.isStereo()
+		let isStereo = self.machine.isStereo
 		if selectedSamplingRate > 0 {
 			// [Re]create the audio queue only if necessary.
 			if self.audioQueue == nil || self.audioQueue.samplingRate != selectedSamplingRate {
@@ -284,9 +281,7 @@ class MachineDocument:
 	/// Delegate message to receive drag and drop files.
 	final func scanTargetView(_ view: CSScanTargetView, didReceiveFileAt URL: URL) {
 		let mediaSet = CSMediaSet(fileAt: URL)
-		if let mediaSet = mediaSet {
-			mediaSet.apply(to: self.machine)
-		}
+		mediaSet.apply(to: self.machine)
 	}
 
 	/// Action for the insert menu command; displays an NSOpenPanel and then segues into the same process
@@ -298,9 +293,7 @@ class MachineDocument:
 			if response == .OK {
 				for url in openPanel.urls {
 					let mediaSet = CSMediaSet(fileAt: url)
-					if let mediaSet = mediaSet {
-						mediaSet.apply(to: self.machine)
-					}
+					mediaSet.apply(to: self.machine)
 				}
 			}
 		}

OSBindings/Mac/Clock Signal/Machine/CSMachine.h

@@ -14,7 +14,7 @@
 #import "CSStaticAnalyser.h"
 
 @class CSMachine;
-@protocol CSMachineDelegate
+@protocol CSMachineDelegate <NSObject>
 - (void)machineSpeakerDidChangeInputClock:(nonnull CSMachine *)machine;
 - (void)machine:(nonnull CSMachine *)machine led:(nonnull NSString *)led didChangeToLit:(BOOL)isLit;
 - (void)machine:(nonnull CSMachine *)machine ledShouldBlink:(nonnull NSString *)led;
@@ -59,7 +59,7 @@ typedef NS_ENUM(NSInteger, CSMachineKeyboardInputMode) {
 - (nullable instancetype)initWithAnalyser:(nonnull CSStaticAnalyser *)result missingROMs:(nullable inout NSMutableArray<CSMissingROM *> *)missingROMs NS_DESIGNATED_INITIALIZER;
 
 - (float)idealSamplingRateFromRange:(NSRange)range;
-- (BOOL)isStereo;
+@property (readonly, getter=isStereo) BOOL stereo;
 - (void)setAudioSamplingRate:(float)samplingRate bufferSize:(NSUInteger)bufferSize stereo:(BOOL)stereo;
 
 - (void)setView:(nullable CSScanTargetView *)view aspectRatio:(float)aspectRatio;

OSBindings/Mac/Clock Signal/Machine/CSMachine.mm

@@ -74,7 +74,7 @@ struct ActivityObserver: public Activity::Observer {
 	__unsafe_unretained CSMachine *machine;
 };
 
-@interface CSMissingROM (Mutability)
+@interface CSMissingROM (/*Mutability*/)
 @property (nonatomic, nonnull, copy) NSString *machineName;
 @property (nonatomic, nonnull, copy) NSString *fileName;
 @property (nonatomic, nullable, copy) NSString *descriptiveName;
@@ -82,53 +82,13 @@ struct ActivityObserver: public Activity::Observer {
 @property (nonatomic, copy) NSArray<NSNumber *> *crc32s;
 @end
 
-@implementation CSMissingROM {
-	NSString *_machineName;
-	NSString *_fileName;
-	NSString *_descriptiveName;
-	NSUInteger _size;
-	NSArray<NSNumber *> *_crc32s;
-}
+@implementation CSMissingROM
 
-- (NSString *)machineName {
-	return _machineName;
-}
-
-- (void)setMachineName:(NSString *)machineName {
-	_machineName = [machineName copy];
-}
-
-- (NSString *)fileName {
-	return _fileName;
-}
-
-- (void)setFileName:(NSString *)fileName {
-	_fileName = [fileName copy];
-}
-
-- (NSString *)descriptiveName {
-	return _descriptiveName;
-}
-
-- (void)setDescriptiveName:(NSString *)descriptiveName {
-	_descriptiveName = [descriptiveName copy];
-}
-
-- (NSUInteger)size {
-	return _size;
-}
-
-- (void)setSize:(NSUInteger)size {
-	_size = size;
-}
-
-- (NSArray<NSNumber *> *)crc32s {
-	return _crc32s;
-}
-
-- (void)setCrc32s:(NSArray<NSNumber *> *)crc32s {
-	_crc32s = [crc32s copy];
-}
+@synthesize machineName=_machineName;
+@synthesize fileName=_fileName;
+@synthesize descriptiveName=_descriptiveName;
+@synthesize size=_size;
+@synthesize crc32s=_crc32s;
 
 - (NSString *)description {
 	return [NSString stringWithFormat:@"%@/%@, %lu bytes, CRCs: %@", _fileName, _descriptiveName, (unsigned long)_size, _crc32s];
@@ -179,17 +139,17 @@ struct ActivityObserver: public Activity::Observer {
 				CSMissingROM *rom = [[CSMissingROM alloc] init];
 
 				// Copy/convert the primitive fields.
-				rom.machineName = [NSString stringWithUTF8String:missing_rom.machine_name.c_str()];
-				rom.fileName = [NSString stringWithUTF8String:missing_rom.file_name.c_str()];
-				rom.descriptiveName = missing_rom.descriptive_name.empty() ? nil : [NSString stringWithUTF8String:missing_rom.descriptive_name.c_str()];
+				rom.machineName = @(missing_rom.machine_name.c_str());
+				rom.fileName = @(missing_rom.file_name.c_str());
+				rom.descriptiveName = missing_rom.descriptive_name.empty() ? nil : @(missing_rom.descriptive_name.c_str());
 				rom.size = missing_rom.size;
 
 				// Convert the CRC list.
-				NSMutableArray<NSNumber *> *crc32s = [[NSMutableArray alloc] init];
+				NSMutableArray<NSNumber *> *crc32s = [[NSMutableArray alloc] initWithCapacity:missing_rom.crc32s.size()];
 				for(const auto &crc : missing_rom.crc32s) {
 					[crc32s addObject:@(crc)];
 				}
-				rom.crc32s = [crc32s copy];
+				rom.crc32s = crc32s;
 
 				// Add to the missing list.
 				[missingROMs addObject:rom];

OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser+TargetVector.h

@@ -8,7 +8,7 @@
 
 #import "CSStaticAnalyser.h"
 
-@interface CSStaticAnalyser (ResultVector)
+@interface CSStaticAnalyser ()
 
 - (Analyser::Static::TargetList &)targets;
 

OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser.h

@@ -8,6 +8,8 @@
 
 #import <Foundation/Foundation.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class CSMachine;
 
 typedef NS_ENUM(NSInteger, CSMachineAppleIIModel) {
@@ -72,7 +74,7 @@ typedef int Kilobytes;
 
 @interface CSStaticAnalyser : NSObject
 
-- (instancetype)initWithFileAtURL:(NSURL *)url;
+- (nullable instancetype)initWithFileAtURL:(NSURL *)url;
 
 - (instancetype)initWithElectronDFS:(BOOL)dfs adfs:(BOOL)adfs;
 - (instancetype)initWithAmstradCPCModel:(CSMachineCPCModel)model;
@@ -85,7 +87,7 @@ typedef int Kilobytes;
 - (instancetype)initWithMacintoshModel:(CSMachineMacintoshModel)model;
 - (instancetype)initWithAtariSTModel:(CSMachineAtariSTModel)model;
 
-@property(nonatomic, readonly) NSString *optionsPanelNibName;
+@property(nonatomic, readonly, nullable) NSString *optionsPanelNibName;
 @property(nonatomic, readonly) NSString *displayName;
 
 @end
@@ -96,3 +98,5 @@ typedef int Kilobytes;
 - (void)applyToMachine:(CSMachine *)machine;
 
 @end
+
+NS_ASSUME_NONNULL_END

OSBindings/Mac/Clock Signal/Machine/StaticAnalyser/CSStaticAnalyser.mm

@@ -39,7 +39,7 @@
 
 		// TODO: could this better be supplied by the analyser? A hypothetical file format might
 		// provide a better name for it contents than the file name?
-		_displayName = [[url pathComponents] lastObject];
+		_displayName = [url.lastPathComponent copy];
 	}
 	return self;
 }

OSBindings/Mac/Clock Signal/MachinePicker/MachinePicker.swift

@@ -140,7 +140,7 @@ class MachinePicker: NSObject {
 
 		switch machineSelector!.selectedTabViewItem!.identifier as! String {
 			case "electron":
-				return CSStaticAnalyser(electronDFS: electronDFSButton!.state == .on, adfs: electronADFSButton!.state == .on)!
+				return CSStaticAnalyser(electronDFS: electronDFSButton!.state == .on, adfs: electronADFSButton!.state == .on)
 
 			case "appleii":
 				var model: CSMachineAppleIIModel = .appleII

OSBindings/Mac/Clock Signal/ROMRequester/CSROMReceiverView.h

@@ -10,7 +10,7 @@
 
 @class CSROMReceiverView;
 
-@protocol CSROMReciverViewDelegate
+@protocol CSROMReciverViewDelegate <NSObject>
 /*!
 	Announces receipt of a file by drag and drop to the delegate.
 	@param view The view making the request.