A demonstration of an inefficiency in mutable array proxies that I think could be improved (rdar://problem/15966921)

AutoNotifyTest.m

// clang -framework Foundation -o AutoNotifyTest AutoNotifyTest.m

/***
Expected results:

willChange:valuesAtIndexes:forKey:
removeObjectFromBarAtIndex:
removeObjectFromBarAtIndex:
removeObjectFromBarAtIndex:
removeObjectFromBarAtIndex:
insertObject:inBarAtIndex:
insertObject:inBarAtIndex:
insertObject:inBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.


Actual results:

willChange:valuesAtIndexes:forKey:
removeObjectFromBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.
willChange:valuesAtIndexes:forKey:
removeObjectFromBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.
willChange:valuesAtIndexes:forKey:
removeObjectFromBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.
willChange:valuesAtIndexes:forKey:
removeObjectFromBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.
willChange:valuesAtIndexes:forKey:
insertObject:inBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.
willChange:valuesAtIndexes:forKey:
insertObject:inBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.
willChange:valuesAtIndexes:forKey:
insertObject:inBarAtIndex:
didChange:valuesAtIndexes:forKey:
-- Observed change.

***/

#import <Foundation/Foundation.h>

@interface Foo : NSObject
// KVO-compliant for mutable array property `bar`
@end

@implementation Foo
{
    NSMutableArray *_bar;
}

- (instancetype)init {
    if ((self = [super init])) {
        _bar = [@[@"one", @"two", @"three", @"four"] mutableCopy];
    }

    return self;
}

- (void)dealloc {
    [_bar release];
    [super dealloc];
}

- (NSUInteger)countOfBar {
    return _bar.count;
}

- (id)objectInBarAtIndex:(NSUInteger)idx { 
    NSLog(@"%@", NSStringFromSelector(_cmd));
    return _bar[idx];
}

- (NSArray *)barAtIndexes:(NSIndexSet *)indexes {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    return [_bar objectsAtIndexes:indexes];
}

- (void)insertObject:(id)o inBarAtIndex:(NSUInteger)idx {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [_bar insertObject:o atIndex:idx];
}

- (void)insertBar:(NSArray *)objs atIndexes:(NSIndexSet *)indexes {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [_bar insertObjects:objs atIndexes:indexes];
}

- (void)removeObjectFromBarAtIndex:(NSUInteger)idx {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [_bar removeObjectAtIndex:idx];
}

- (void)removeBarAtIndexes:(NSIndexSet *)indexes {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [_bar removeObjectsAtIndexes:indexes];
}

- (void)willChangeValueForKey:(NSString *)key {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [super willChangeValueForKey:key];
}

- (void)willChange:(NSKeyValueChange)change valuesAtIndexes:(NSIndexSet *)indexes forKey:(NSString *)key {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [super willChange:change valuesAtIndexes:indexes forKey:key];
}

- (void)didChangeValueForKey:(NSString *)key {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [super didChangeValueForKey:key];
}

- (void)didChange:(NSKeyValueChange)change valuesAtIndexes:(NSIndexSet *)indexes forKey:(NSString *)key {
    NSLog(@"%@", NSStringFromSelector(_cmd));
    [super didChange:change valuesAtIndexes:indexes forKey:key];
}

@end

@interface AnObserver : NSObject
@property (assign) Foo *f;
@end

@implementation AnObserver
{
    Foo *_f;
}

static void *ctx = &ctx;

- (Foo *)f {
    return _f;
}

- (void)setF:(Foo *)f {
    [_f removeObserver:self forKeyPath:@"bar" context:ctx];
    [_f release];
    _f = [f retain];
    [_f addObserver:self forKeyPath:@"bar" options:0 context:ctx];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)obj change:(NSDictionary *)change context:(void *)context {
    if (context == ctx)
        NSLog(@"-- Observed change.");
    else
        [super observeValueForKeyPath:keyPath ofObject:obj change:change context:context];
}
@end

int main(int argc, char **argv) {
    @autoreleasepool {
        Foo *f = [Foo new];
        AnObserver *obs = [AnObserver new];
        obs.f = f;

        // This should be much more efficient--while inside the call to -setArray:, the mutable array proxy should send _ONE_ notification, then suspend auto notifications while calling the indexed to-many accessors.
        NSMutableArray *arr = [f mutableArrayValueForKey:@"bar"];
        [arr setArray:@[@"three", @"five", @"one"]];
    }
    return 0;
}