investigate how mutable dictionaries grow.

mutabledict.m

//
//  main.m
//  nsmutabledict
//
//  Created by Stephen Altamirano on 5/29/12.
//

#import <Foundation/Foundation.h>

NSMutableArray* dict_keys(NSMutableDictionary* d)
{
    NSMutableArray* a = [NSMutableArray arrayWithCapacity:[d count]];
    for (NSString* key in d)
    {
        [a addObject:key];
    }
    return a;
}

void compare_keys(NSArray* arr1, NSArray* arr2)
{
    if (!arr1)
    {
        return;
    }
    
    NSUInteger total_keys = [arr2 count];
    int skipped = 0;
    for (int i=0; i < total_keys - 1; i++)
    {
        if ([arr2 objectAtIndex:i] != [arr1 objectAtIndex:i - skipped])
        {
            if (skipped == 0) 
            {
                skipped += 1;
            }
            else
            {
                NSLog(@"rehashed at insertion %ld", total_keys);
                return;
            }
        }
    }
}

void run()
{
    NSMutableDictionary* dict = [NSMutableDictionary dictionary];
    NSMutableArray* last_keys = nil;
    NSMutableArray* keys = nil;
    for (int i = 0; i < 10000; i++)
    {
        keys = dict_keys(dict);
        compare_keys(last_keys, keys);
        last_keys = keys;
        [dict setObject:[NSNumber numberWithInt:i]
                 forKey:[NSString stringWithFormat:@"%d", i]];
    }
}

int main (int argc, const char * argv[])
{

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    run();
    [pool drain];
    return 0;
}