Re: When do I need to override hash?
Re: When do I need to override hash?
- Subject: Re: When do I need to override hash?
- From: Clark Cox <email@hidden>
- Date: Wed, 19 Aug 2009 18:40:51 -0700
On Wed, Aug 19, 2009 at 6:19 PM, Seth Willits<email@hidden> wrote:
> On Aug 19, 2009, at 4:28 PM, Gideon King wrote:
>
>> So do I need to override hash too? If so, are there any recommendations as
>> to how to determine the hash easily?
>
> I probably shouldn't admit this, but I've yet to override hash and have yet
> to notice any problems. The docs say I should, so I realize I likely should,
> but I would really like a concrete reason to do so. I've never called hash,
> nor seen it ever called by anyone else's code. I assume the frameworks call
> it from somewhere, but where?
If you've ever put those objects in an associative or hashing
container (NSSet, NSDictionary keys, NSHashMap NSHashTable, etc.),
you're probably sitting on obscure, hard to find bugs.
In general, if you override -isEqual:, you should override -hash. Period.
--
Clark S. Cox III
email@hidden
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