HashBuilder

Used to build a hash result from contributed objects or hashes (presumably properties on your object which should be considered in the isEqual: override). The intention is for the hash result to be returned from an override to the NSObject - (NSUInteger)hash method.

Installing

If you're using CocoPods it's as simple as adding this to your Podfile:

pod 'HashBuilder', '~> 1.0'

otherwise, simply add the contents of the HashBuilder subdirectory to your project.

Documentation

To use, create a HashBuilder object, contribute to it, then query the 'builtHash' property for the resulting hash.

- (NSUInteger)hash
{
	HashBuilder *builder = [HashBuilder builder];

	[builder contributeObject:self.objectID];
	[builder contributeObject:self.occurredDate];
	[builder contributeObject:self.type];
	[builder contributeObject:self.objectURL];
	[builder contributeObject:self.tags];
	[builder contributeObject:self.count];

	NSUInteger retVal = builder.builtHash;

	return retVal;
}

It is prudent to consider the same properties when overriding your - (BOOL)isEqual:(id)object method as well.

NOTE: The order of contribution will change the resulting hash, even if all the same values are contributed. For example:

HashBuilder *builder1 = [HashBuilder builder];
[builder1 contributeObject:@"a"];
[builder1 contributeObject:[NSNumber numberWithInteger:12345]];
NSUInteger hash1 = builder1.builtHash;

HashBuilder *builder2 = [HashBuilder builder];
[builder2 contributeObject:[NSNumber numberWithInteger:12345]];
[builder2 contributeObject:@"a"];
NSUInteger hash2 = builder2.builtHash;

hash1 != hash2

Disclaimer and Licence

• This work makes use of techniques and concepts presented by Mike Ash in his post entitled Implementing Equality and Hashing
• This work is licensed under the Creative Commons Attribution 3.0 Unported License. Please see the included LICENSE.txt for complete details.

About

A professional iOS engineer by day, my name is Levi Brown. Authoring a technical blog grokin.gs, I am reachable via:

Twitter @levigroker
EMail [email protected]

Your constructive comments and feedback are always welcome.