3 ms·

They are immutable by default, but it's expensive to get a new data structure with some changes in it. That's what persistent data structures for. I personally

• jawngee 12y ago
  Expensive how? Your classes are 10-20x slower in every other way, which definitely would offset any imaginary expense you think calling `mutableCopy` costs. I have to tell you in 10+ years of writing Objective-C where I was like [myArray mutableCopy] is super slow, I need a replacement. I've wished for an NSOrderedDictionary though.
  • astashov 12y ago
    10-20x slower means it makes sense to use a persistent map when the size of your Dictionary is > 20 records. Then, // yourDictionary is NSMutableDictionary, [yourDictionary count] > 20 NSMutableDictionary *mutable = [yourDictionary mutableCopy]; mutable[@"old_key"] = @"new_value"; NSDictionary *changedDict = [NSDictionary dictionaryWithDictionary:mutable]; will be slower than // yourDictionary is AAPersistentHashMap, [yourDictionary count] > 20 AAPersistentHashMap *changedDict = [yourDictionary setObject:@"new_value" forKey:@"old_key"]; Remember, you need to get another immutable map, which is a modified version of the original, preferably memory-efficient, which means we want to reuse the unchanged keys/values of the original map.