Objective-C Literals, part 2 support files.

BNRDiggyDict.h

#import <Foundation/Foundation.h>

@interface BNRDiggyDict : NSObject

// React to object indexing.  Would be nice to have a @protocol for this
- (id) objectForKeyedSubscript: (id) key;
- (void) setObject: (id) thing  forKeyedSubscript: (id<NSCopying>) key;

// And for fun, it also can react to scalar indexing.
// Returns the N'th key of the top-level collection.
- (id) objectAtIndexedSubscript: (NSInteger) index;

@end // BWDiggyDict

BNRDiggyDict.m

#import "BNRDiggyDict.h"

@interface BNRDiggyDict () {
    NSMutableDictionary *_rootDictionary;
}

@end // BWDiggyDict


@implementation BNRDiggyDict

- (id) init {
    if ((self = [super init])) {
        _rootDictionary = [NSMutableDictionary dictionary];
    }

    return self;

} // init


- (NSString *) description {
    return [_rootDictionary description];
} // description



- (NSMutableDictionary *) innerDictionaryForSplitKey: (NSArray *) splitKey {

    NSMutableDictionary *interim = _rootDictionary;

    for (int i = 0; i < splitKey.count - 1; i++) {
        id key = [splitKey objectAtIndex: i];
        NSMutableDictionary *next = interim[key];
        if (next == nil) {
            next = [NSMutableDictionary dictionary];
            interim[key] = next;
        }
        interim = next;
    }
    
    return interim;

} // innerDictionaryForSplitKey


- (id) objectForKeyedSubscript: (id) key {
    if (![key respondsToSelector: @selector(componentsSeparatedByString:)]) {
        return nil;
    }

    // Use slashes rather than periods since we're not really doing KVC
    NSArray *splitKey = [key componentsSeparatedByString: @"/"];

    NSMutableDictionary *dict = [self innerDictionaryForSplitKey: splitKey];
    id leafKey = [splitKey lastObject];
    id result = dict[leafKey];

    return result;
    
} // objectForKeyedSubscript


- (void) setObject: (id) thing  forKeyedSubscript: (id<NSCopying>) key {
    id idKey = (id) key;  // Strip off <NSCopying> so we can send it other messages.
    if (![idKey respondsToSelector: @selector(componentsSeparatedByString:)]) {
        return;
    }

    // Use slashes rather than periods since we're not really doing KVC
    NSArray *splitKey = [idKey componentsSeparatedByString: @"/"];

    NSMutableDictionary *dict = [self innerDictionaryForSplitKey: splitKey];
    id leafKey = [splitKey lastObject];

    [dict setObject: thing  forKey: leafKey];

} // setObject forKeyedSubscript


// And just for fun
- (id) objectAtIndexedSubscript: (NSInteger) index {
    NSArray *keys = [_rootDictionary.allKeys
                                    sortedArrayUsingSelector: @selector(compare:)];
    return [keys objectAtIndex: index];
} // objectAtIndexedSubscript


@end // BWDiggyDict

BNRNegativeArray.h

#import <Foundation/Foundation.h>

@interface BNRNegativeArray : NSObject

// Necessary to declare these.  Would be nice to have a protocol to adopt.
- (id) objectAtIndexedSubscript: (NSInteger) index;
- (void) setObject: (id) thing  atIndexedSubscript: (NSInteger) index;

@end // BWNegativeArray

BNRNegativeArray.m

#import "BNRNegativeArray.h"


@interface BNRNegativeArray () {
    NSMutableArray *_backingstore;
}

@end // extension


@implementation BNRNegativeArray

- (id) init {
    if ((self = [super init])) {
        _backingstore = [NSMutableArray array];
    }
    return self;
} // init


- (NSString *) description {
    return [_backingstore description];
} // descriptioin


- (id) objectAtIndexedSubscript: (NSInteger) index {
    if (index < 0) index = _backingstore.count + index;

    return [_backingstore objectAtIndex: index];

} // objectAtIndexedSubscript


- (void) setObject: (id) thing  atIndexedSubscript: (NSInteger) index {
    if (index < 0) index = _backingstore.count + index;

    // Mutable array only allows setting the first-empty-index, like
    // -insertObject:atIndex:.  Any past that throws a range exception.
    // So let's be different and fill in intervening spaces with [NSNull null]
    // If you want to see @NULL, dupe rdar://10892975

    NSInteger toAdd = index - _backingstore.count;;
    for (int i = 0; i < toAdd; i++) {
        [_backingstore addObject: [NSNull null]];
    }

    if (index >= _backingstore.count) {
        [_backingstore addObject: thing];
    } else {
        [_backingstore replaceObjectAtIndex: index  withObject: thing];
    }

} // setObject atIndexedSubscript

@end // BWNegativeArray

main.m

#import <Foundation/Foundation.h>

#import "BNRNegativeArray.h"
#import "BNRDiggyDict.h"

int main (int argc, const char * argv[]) {
    @autoreleasepool {
        BNRNegativeArray *negatory = [[BNRNegativeArray alloc] init];
        negatory[0] = @"hi";
        negatory[1] = @"ohai";
        negatory[0] = @"obai";
        negatory[10] = @"end!";
        NSLog (@"negatory: %@", negatory);
        
        NSLog (@"0 - %@", negatory[0]);
        NSLog (@"5 - %@", negatory[5]);
        NSLog (@"10 - %@", negatory[10]);
        NSLog (@"-1 - %@", negatory[-1]);
        NSLog (@"-10 - %@", negatory[-10]);
        NSLog (@"-11 - %@", negatory[-11]);


        BNRDiggyDict *dauchs = [[BNRDiggyDict alloc] init];
        dauchs[@"i can has"] = @"cheezburger";
        NSLog (@"badger: %@", dauchs);

        dauchs[@"for/great/justice"] = @"every 'ZIG'";
        NSLog (@"badger: %@", dauchs);

        NSLog (@"TAKE OFF %@", dauchs[@"for/great/justice"]);

        // Exercise a scalar accessor on the diggydict
        dauchs[@"Alphabet"] = @"A";
        dauchs[@"Badger"] = @"B";
        dauchs[@"Carnivorous Tofu"] = @"Nom!";
        NSLog (@"second key: %@", dauchs[2]);
    }
    return 0;
} // main