It’s possible, however, to bring over some of the ideas from the Land of Lisp to other languages. Indeed this is essentially what has been happening for the past several decades, people just call it something different (“a new language”, or “new features”). Today, I’d like to show what happens when you bring one such idea to Objective-C:

It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures.

—Alan Perlis

PXSourceList is a wonderful and popular Cocoa view for creating iTunes-like source lists created by Alex Rozanski:

Unfortunately, the example code that created the screenshot above suffers from a very common programming paradigm called Object Oriented Programming (OOP). The OOP paradigm has dominated Earth’s developers for the past several decades. I used to follow (and teach!) it, but after learning Clojure, I’ve changed my mind. I now agree with the Alex Rozanski quote above and Rich Hickey: it is better to have a small number of core data structures (preferably immutable) that are manipulated by hundreds of functions.

For this post, I will focus on just one of the many benefits of dropping the OOP perspective: code brevity.

The chief source responsible for the screenshot above is copied below. My point here isn’t to ask you to actually read through all of it, just note its size.

Instead of this:

// =========================
// = File SourceListItem.h =
// =========================

#import <Cocoa/Cocoa.h>

@interface SourceListItem : NSObject {
    NSString *title;
    NSString *identifier;
    NSImage *icon;
    NSInteger badgeValue;

    NSArray *children;
}

@property (nonatomic, copy) NSString *title;
@property (nonatomic, copy) NSString *identifier;
@property (nonatomic, retain) NSImage *icon;
@property NSInteger badgeValue;

@property (nonatomic, copy) NSArray *children;

//Convenience methods
+ (id)itemWithTitle:(NSString*)aTitle identifier:(NSString*)anIdentifier;
+ (id)itemWithTitle:(NSString*)aTitle identifier:(NSString*)anIdentifier icon:(NSImage*)anIcon;

- (BOOL)hasBadge;
- (BOOL)hasChildren;
- (BOOL)hasIcon;

@end

// =========================
// = File SourceListItem.m =
// =========================

#import "SourceListItem.h"

@implementation SourceListItem

@synthesize title;
@synthesize identifier;
@synthesize icon;
@synthesize badgeValue;
@synthesize children;

#pragma mark -
#pragma mark Init/Dealloc/Finalize

- (id)init
{
    if(self=[super init])
    {
        badgeValue = -1;    //We don't want a badge value by default
    }

    return self;
}

+ (id)itemWithTitle:(NSString*)aTitle identifier:(NSString*)anIdentifier
{
    SourceListItem *item = [SourceListItem itemWithTitle:aTitle identifier:anIdentifier icon:nil];

    return item;
}

+ (id)itemWithTitle:(NSString*)aTitle identifier:(NSString*)anIdentifier icon:(NSImage*)anIcon
{
    SourceListItem *item = [[[SourceListItem alloc] init] autorelease];

    [item setTitle:aTitle];
    [item setIdentifier:anIdentifier];
    [item setIcon:anIcon];

    return item;
}

- (void)dealloc
{
    [title release];
    [identifier release];
    [icon release];
    [children release];

    [super dealloc];
}

- (void)finalize
{
    title = nil;
    identifier = nil;
    icon = nil;
    children = nil;

    [super finalize];
}

#pragma mark -
#pragma mark Custom Accessors

- (BOOL)hasBadge
{
    return badgeValue!=-1;
}

- (BOOL)hasChildren
{
    return [children count]>0;
}

- (BOOL)hasIcon
{
    return icon!=nil;
}

@end

// ======================
// = File AppDelegate.m =
// ======================

#import "AppDelegate.h"
#import "SourceListItem.h"

@implementation AppDelegate

#pragma mark -
#pragma mark Init/Dealloc

- (void)awakeFromNib
{
    [selectedItemLabel setStringValue:@"(none)"];

    sourceListItems = [[NSMutableArray alloc] init];

    //Set up the "Library" parent item and children
    SourceListItem *libraryItem = [SourceListItem itemWithTitle:@"LIBRARY" identifier:@"library"];
    SourceListItem *musicItem = [SourceListItem itemWithTitle:@"Music" identifier:@"music"];
    [musicItem setIcon:[NSImage imageNamed:@"music.png"]];
    SourceListItem *moviesItem = [SourceListItem itemWithTitle:@"Movies" identifier:@"movies"];
    [moviesItem setIcon:[NSImage imageNamed:@"movies.png"]];
    SourceListItem *podcastsItem = [SourceListItem itemWithTitle:@"Podcasts" identifier:@"podcasts"];
    [podcastsItem setIcon:[NSImage imageNamed:@"podcasts.png"]];
    [podcastsItem setBadgeValue:10];
    SourceListItem *audiobooksItem = [SourceListItem itemWithTitle:@"Audiobooks" identifier:@"audiobooks"];
    [audiobooksItem setIcon:[NSImage imageNamed:@"audiobooks.png"]];
    [libraryItem setChildren:[NSArray arrayWithObjects:musicItem, moviesItem, podcastsItem,
                              audiobooksItem, nil]];

    //Set up the "Playlists" parent item and children
    SourceListItem *playlistsItem = [SourceListItem itemWithTitle:@"PLAYLISTS" identifier:@"playlists"];
    SourceListItem *playlist1Item = [SourceListItem itemWithTitle:@"Playlist1" identifier:@"playlist1"];

    //Create a second-level group to demonstrate
    SourceListItem *playlist2Item = [SourceListItem itemWithTitle:@"Playlist2" identifier:@"playlist2"];
    SourceListItem *playlist3Item = [SourceListItem itemWithTitle:@"Playlist3" identifier:@"playlist3"];
    [playlist1Item setIcon:[NSImage imageNamed:@"playlist.png"]];
    [playlist2Item setIcon:[NSImage imageNamed:@"playlist.png"]];
    [playlist3Item setIcon:[NSImage imageNamed:@"playlist.png"]];

    SourceListItem *playlistGroup = [SourceListItem itemWithTitle:@"Playlist Group" identifier:@"playlistgroup"];
    SourceListItem *playlistGroupItem = [SourceListItem itemWithTitle:@"Child Playlist" identifier:@"childplaylist"];
    [playlistGroup setIcon:[NSImage imageNamed:@"playlistFolder.png"]];
    [playlistGroupItem setIcon:[NSImage imageNamed:@"playlist.png"]];
    [playlistGroup setChildren:[NSArray arrayWithObject:playlistGroupItem]];

    [playlistsItem setChildren:[NSArray arrayWithObjects:playlist1Item, playlistGroup,playlist2Item,
                                playlist3Item, nil]];

    [sourceListItems addObject:libraryItem];
    [sourceListItems addObject:playlistsItem];

    [sourceList reloadData];
}

By using “special” dictionaries, we can greatly reduce code size, and enhance flexibility

Clojure has the concept of “records”. These are basically “special dictionaries” (AKA maps). Clojure uses maps/dictionaries all over the place, because it realizes that it’s not only not necessary to create a new class for every type of data you have, but it’s counter-productive.

Today I spent some time adapting the idea of Clojure’s records into its Objective-C equivalent simply through the creation of categories on the NSDictionary and NSMutableDictionary classes. The result is that I was able to reproduce the screenshot above with the following code (equivalent sections to the ones above):

// ======================
// = File AppDelegate.m =
// ======================

#import "AppDelegate.h"

@protocol SourceListItem
@property (nonatomic, retain) NSString *title;
@property (nonatomic, retain) NSString *identifier;
@property (nonatomic, retain) NSNumber *type;
@property (nonatomic, retain) NSImage *icon;
@property (nonatomic, retain) NSMutableArray *children;
@end

@implementation AppDelegate

- (void)awakeFromNib
{
    sourceListItems = [[NSMutableArray alloc] initWithObjects:
                       _MD(@"title", @"LIBRARY",
                           @"identifier", @"library",
                           @"children",
                           NSARY(_MD(@"title", @"Music",
                                     @"identifier", @"music",
                                     @"icon", NSIMG(@"music")),
                                _MD(@"title", @"Movies",
                                    @"identifier", @"movies",
                                    @"icon", NSIMG(@"movies")),
                                 _MD(@"title", @"Podcasts",
                                     @"identifier", @"podcasts",
                                     @"icon", NSIMG(@"podcasts")),
                                 _MD(@"title", @"Audiobooks",
                                     @"identifier", @"audiobooks",
                                     @"icon", NSIMG(@"audiobooks")))),
                       _MD(@"title", @"PLAYLISTS",
                           @"identifier", @"playlists",
                           @"children",
                           NSARY(_MD(@"title", @"Playlist1",
                                     @"identifier", @"playlist1",
                                     @"icon", NSIMG(@"playlist")),
                                 _MD(@"title", @"Playlist Group",
                                     @"identifier", @"playlistgroup",
                                     @"icon", NSIMG(@"playlistFolder"),
                                     @"children",
                                     NSARY(_MD(@"title", @"Child Playlist",
                                               @"identifier", @"childplaylist",
                                               @"icon", NSIMG(@"playlist")))),
                                 _MD(@"title", @"Playlist1",
                                     @"identifier", @"playlist1",
                                     @"icon", NSIMG(@"playlist")),
                                 _MD(@"title", @"Playlist1",
                                     @"identifier", @"playlist1",
                                     @"icon", NSIMG(@"playlist")))),
                       nil];
    [sourceList reloadData];
}

Not only is the code above more flexible and significantly shorter, but it’s clearer as well! You can practically visualize the GUI’s structure from the code itself!

The rest of the code (related to the delegate methods) is essentially equivalent, except it’s again, shorter.

“Magic” Dictionaries with Properties!

Dictionaries are created using the _MD and _D macros (for creating mutable and immutable dictionaries, respectively). These are plain old standard Foundation dictionaries. They can be saved to the hard disk, read back, key-value coded, etc. The reason for the macros is code brevity and because they use a new dictionaryWithKeysAndObjects: method that’s added to all dictionaries through the categories (I have no idea why Apple’s engineers throught it would be better to have values come before keys as with dictionaryWithObjectsAndKeys:…).

Next, let’s have a look at how dictionary values are manipulated and obtained. Most semi-intelligent languages have a map literals and simple syntax for fetching and setting map key/value pairs. Objective-C has no such intelligence imparted to it. However, it does have the very nifty forwardInvocation: mechanism. By combining forwardInvocation: with Objective-C protocols and properties, it’s possible to create “Objective-C records”.

Instead of this:

- (NSUInteger)sourceList:(PXSourceList*)sourceList numberOfChildrenOfItem:(id)item
{
    //Works the same way as the NSOutlineView data source: `nil` means a parent item
    if(item==nil) {
        return [sourceListItems count];
    }
    else {
        return [[item children] count];
    }
}

We can now use the dot-syntax notation to do this:

- (NSUInteger)sourceList:(PXSourceList*)sourceList numberOfChildrenOfItem:(id<SourceListItem>)item
{
    return item ? [item.children count] : [sourceListItems count];
}

Behind the scenes, item.children is turned into [item objectForKey:@"children"].

Setting values is also done through the standard dot-notation of Objective-C properties:

- (void)sourceList:(PXSourceList*)aSourceList setObjectValue:(id)object forItem:(id<SourceListItem>)item
{
    item.title = object;
}

Grab on Github

You’ll find the project for TERecord here, and the converted example of PXSourceList here.

So, you want to quad-boot your Mac? What could possibly go wrong?

This post explores that question.

Motivation

After upgrading to the latest Unibody, I decided to turn my old MacBook Pro into the ultimate testing environment. My goal was to be able to test and develop software for Tiger, Leopard, Snow Leopard, Windows XP, and possibly other operating systems in the future (Windows 7, Ubuntu, etc., although that might require Grub).

Setting Up The Partitions

I originally thought this entire process would be a simple matter of creating partitions and installing each OS on its respective partition (Hah!). The plan was to use iPartition to create this setup without erasing my Snow Leopard install:

To do this, I had to first run iDefrag (also made by Coriolis Systems) to compact the Snow Leopard install. Then I could non-destructively resize its partition and add the rest.

iPartition wasn’t able to create an NTFS partition so I left the Windows partition unformatted, everything else was formatted as HFS+, journaled.

I had saved a Windows install using Winclone, so I went to try to restore that. That failed because Winclone needs the partition to be formatted first.

I tried using Boot Camp Assistant (BCA) to create the NTFS partition, but BCA greeted me with this error (for the Googlers): “The startup disk cannot be partitioned or restored to a single partition.”

To get around this error you probably could use iPartition to create a single HFS+ partition and install Snow Leopard on it. You would need to use iPartition because iPartition lets you create partitions while leaving free space on the drive, and remember, we need that space to create additional partitions for the other operating systems. Disk Utility cannot leave “unpartitioned space” on the drive, and therefore you’d end up creating more than one partition before running BCA, which would then refuse to do its thing.

I went a different route though, as I discovered that by installing NTFS-3G (the free Open Source version), I could create NTFS partitions using Disk Utility. So I partitioned the entire drive, this time using Disk Utility, and was able to successfully restore Windows to the NTFS partition using Winclone.

That was the easy part though.

Fragile Windows

Restoring Windows is one thing, getting it to boot is another. Upon rebooting to check the XP install, I was greeted with a black screen and error message along the lines of “No bootable device available.”

After searching Google I came across this hint on how to triple-boot your system. The comments section were particularly helpful, and led me to investigate the boot.ini file as a possible source of the problem.

The boot.ini file, for some reason, specifies what partition number it’s located on. My Windows partition was in the wrong location, and it didn’t like that. So I followed their suggestions and edited the file using emacs, and played around with the number. I tried every single number between 1 and 6, and even zero (out of desperation), none would satisfy Windows.

At some later point, after much formatting and reinstalling, I actually got Windows to boot, only to be greeted by a blue screen instead of a black screen, which flashed too quickly for me to read and then the computer restarted itself.

Although I don’t have a complete list of my Googles during this time, here’s what I was able to dig up from Firefox’s history, hopefully it will save a fellow Googler or two:

• chkdsk “volume appears to contain”
• “windows could not start” hal.dll
• windows xp recovery console
• “no bootable device” boot.ini bootcamp
• boot camp UNMOUNTABLE_BOOT_VOLUME
• “there is no operating system installed in this virtual machine” (That’s from Parallels)

The “Right” Partition

Here’s what I now know. Editing boot.ini may or may not work. In my case (with Windows XP) it definitely did not. Prior to embarking on this journey, you need to decide ahead of time what to install on the first two partitions, because the third has to be Windows. In Disk Utility, partitions start from the top:

I’m pretty sure Windows must be installed on the third partition. It’s either that or the second one. For me right now, the third partition has done the trick.

Now, with a working WIndows install, I know how to verify the number in the boot.ini file. It does in fact correspond to the partition number as specified in the output of diskutil list, and/or df. It’s one greater than the number you’d expect if you were just going by Disk Utility’s GUI. Here’s the output from the quad-booting laptop as it is now, showing it as partition #4:

Last login: Sun Jun 13 19:22:13 on console
Macintosh:~ gslepak$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *200.0 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Snow Leopard            49.7 GB    disk0s2
   3:                  Apple_HFS Leopard                 32.6 GB    disk0s3
   4:       Microsoft Basic Data Windows                 29.2 GB    disk0s4
   5:                  Apple_HFS Tiger                   20.6 GB    disk0s5
Macintosh:~ gslepak$ df
Filesystem    512-blocks     Used Available Capacity  Mounted on
/dev/disk0s2    97069312 23384096  73173216    25%    /
devfs                218      218         0   100%    /dev
map -hosts             0        0         0   100%    /net
map auto_home          0        0         0   100%    /home
/dev/disk0s3    63741456 24106640  39634816    38%    /Volumes/Leopard
/dev/disk0s4    57012216 29356408  27655808    52%    /Volumes/Windows
/dev/disk0s5    40174016 15283088  24890928    39%    /Volumes/Tiger

Stubborn Tiger

Not to be outdone by its Redmond counterpart, Mac OS 10.4 Tiger turned out to be even more difficult to install.

First, the install disk that came with the computer (which had 10.4.9) refused to be recognized. It spun for a little while and was then spit out. So I inserted it into my PowerMac figuring I could just install over Target Disk Mode, but it refused to run because Apple watermarks these DVDs so that they only work on the exact same kind of computer.

Fortunately, I had another Tiger install disk that did work with any Mac. It was only after the installation finished (over Target Disk Mode, again), that I realized it was a PPC-only install, causing the Intel laptop to kernel panic on boot.

Feeling defeated, I went for a jog, during which I realized that I could insert the Intel install disk into my Unibody MacBook Pro, copy it onto an external hard disk, and boot off of that, thereby bypassing the flaky SuperDrive on the old MacBook Pro.

That outta do it, right?

And it did! Now I just had to figure out what to do about the crazy blue and black stripes on the screen that made it impossible to see the installer.

You see, this laptop, like most of its kind, was affected by the infamous NVIDIA 8600GT bug that completely wiped out its display capabilities. Apple kindly replaced the logic board but, in doing so, apparently killed its compatibility with Tiger.

You would think that by this point any sane person would have called it a day, but it was far too late for me. My OCD was in overdrive, and I had become sort of obsessed with solving this problem. Failure was not an option… not yet at least.

Verbose mode showed the following error:

GFX0 matching specific fails

Google wasn’t very helpful here unfortunately, but I figured that there was a missing or outdated graphics driver. So I spent some time copying and replacing kernel extensions from my Leopard install (which had finished without problems) into the Tiger installation drive. This took a rather long time, as each time I changed a kernel extension I had to reboot to see if the fix took. I had to replace them one at a time so as to avoid potentially compounding the problem (as kernel extensions have dependencies).

Sidenote: If you ever find yourself switching out kernel extensions, don’t forget to delete the cache files ‘Extensions.mkext’ and ‘Extensions.kextcache’ each time you do. These files may or may not be present in the /System/Library folder, depending on the OS version.

Eventually I realized this was stupid, because I could simply run the OS install by running the OSInstall.mpkg from within Snow Leopard:

The installer ran (and hung at the end, of course) but it looked like it had installed everything that was necessary so I rebooted again from the Tiger disk.

I should mention that sometimes the disks that I needed to boot from did not appear in the Startup Disk preference pane, despite being bootable. I got around that by running the bless command on the volume:

sudo bless --mount /Volumes/Tiger --setBoot --nextonly

I booted into Tiger and again was greeted with its unreadable blue stripes, and by now the all too familiar setup theme music. Curses!

I decided to install the 10.4.11 Combo Update from Snow Leopard, thinking it might contain the proper drivers. The download link on Apple’s site was broken, but by this point the random problems no longer surprised me. After some searching I finally found a working link to it. Too bad though, the update did not fix the problem.

It then dawned upon me that this was all a test. God was testing me, to see how badly I wanted to install the outdated operating system, and whether I really did possess the geek-credentials I claimed to have.

So I went back to the old plan of replacing kernel extensions.

I copied a bunch of extensions over from Leopard that I thought might fix the problem without causing too many dependency issues. While that did get rid of the error message, and Tiger no longer sported blue and black stripes, instead, I saw only the black and white text of the verbose screen while the Tiger setup music played in the background, taunting me.

I proceeded to replace the kernel extensions with the originals, one-by-one, hoping to find the one that was responsible for the missing error message. After what had to be at least an hour I finally noticed it: the GFX0 error message was back, and it was after I had replaced NVDAResman.kext with its original.

Intrigued, I restored the entire Extensions folder back to its original state and replaced just NVDAResman.kext.

Success!!

Almost! There was one loose-end left to fix. After logging into my account on Tiger, I got a couple of error messages complaining about NVDANV50Hal.kext and GeForce.kext not loading properly. Simply removing them from the /System/Library/Extensions did the trick, with no noticeable ill effects (I tried replacing them with the ones from the Leopard install, but that didn’t work).

As a finishing touch, I used iPartition to shrink the Tiger partition. This way I won’t have to run iDefrag on it if I decide to install additional operating systems in the future (like 10.7). Here’s how it looks in Disk Utility:

Hopefully this post will save someone a headache, or two.

TESetupAssistant was born during my work on the 2.0 update to Espionage, when I discovered that many of its UI elements could stand to benefit from a generic setup assistant class.

The gallery below shows some of the places in Espionage where we use TESetupAssisant, illustrating its versatility:

You can create these sorts of UIs very quickly and use them wherever the user needs to complete a series of steps, or even a single step (as shown in the first image above). Here’s a basic overview of it:

There are two main classes: TESetupAssistant and TEBaseAssistant. TESetupAssistant is associated with a nib file that determines the overall layout. It manages a one or more assistants, each of which inherit from TEBaseAssistant. Each TEBaseAssistant subclass has its own nib file, usually just containing a single NSView container object.

Example of a Modal Assistant

Here’s an example of a very simple assistant using the minified UI and running modally:

And here is all the code needed to create it:

#import <Cocoa/Cocoa.h>
#import "TESetupAssistant.h"

@interface MiniAssistant : TEBaseAssistant {
    IBOutlet NSTextField *textField;
}
@end

@implementation MiniAssistant
- (NSArray *)orderedSteps
{
    return [NSArray arrayWithObject:@"Mini Step"];
}
- (void)start
{
    [[controller nextButton] setTitle:@"Finish"];
    [textField setStringValue:NSSTR_FMT(
        "Hi there! I'm a mini-assistant %srunning modally!",
        [controller modal] ? "" : "not ")
    ];
}
@end

// To run it modally is just 4 lines of code (somewhere):

TESetupAssistant *sa = [[[TESetupAssistant alloc] initMini] autorelease];
[sa setModal:YES];
[sa addAssistant:[MiniAssistant assistant]];
[sa run];

Notice that we don’t even need to load the nib file. That’s because our nib file is named after our assitant (MiniAssistant.nib). You can of course override the -assistantNib method to specify a different one, but that illustrates one key aspect of TESetupAssistant, and that is that there are sensible defaults for almost everything, allowing you to quickly throw together these kinds of interfaces.

Get It On Github

I’m releasing TESetupAssistant as open source under a liberal license (just an attribution is asked for), and I’ve included a little demo app to help you hit the ground running. You can download it on github.

If you use it in your application I’d love to know! Shoot us an email or post a comment below and I’ll place a link here to your app.

Enjoy!

You can follow me on twitter here.