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Re: When do I need to override hash?
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Re: When do I need to override hash?


  • Subject: Re: When do I need to override hash?
  • From: Jean-Daniel Dupas <email@hidden>
  • Date: Fri, 21 Aug 2009 11:20:52 +0200


No, not true.

Key values cannot be mutated while used in a collection, period.

Correct.


Excuse my intrusion in this discussion, but I don't really understand why 'isEqual:' and 'compare:' results must not change when an object is used as key.
My though was that as long as the hash remain the same, it should not be an issue. I don't see any case where it may be useful, but don't see why it would be illegal ?





Forget my question, I just see this comment from Quincey which give me an answer.

[Actually, for all I know, key values *can* be mutated while used in a
collection, provided the hash value doesn't change, but even if it
technically feasible it sounds so un-useful I'd argue it's better just
to assert that it's not allowed.]


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References: 
 >When do I need to override hash? (From: Gideon King <email@hidden>)
 >Re: When do I need to override hash? (From: Seth Willits <email@hidden>)
 >Re: When do I need to override hash? (From: David Duncan <email@hidden>)
 >Re: When do I need to override hash? (From: Clark Cox <email@hidden>)
 >Re: When do I need to override hash? (From: Bryan Henry <email@hidden>)
 >Re: When do I need to override hash? (From: Clark Cox <email@hidden>)
 >Re: When do I need to override hash? (From: Kyle Sluder <email@hidden>)
 >Re: When do I need to override hash? (From: Shawn Erickson <email@hidden>)
 >Re: When do I need to override hash? (From: Clark Cox <email@hidden>)
 >Re: When do I need to override hash? (From: Kyle Sluder <email@hidden>)
 >Re: When do I need to override hash? (From: Clark Cox <email@hidden>)
 >Re: When do I need to override hash? (From: Alastair Houghton <email@hidden>)
 >Re: When do I need to override hash? (From: Seth Willits <email@hidden>)
 >Re: When do I need to override hash? (From: Quincey Morris <email@hidden>)
 >Re: When do I need to override hash? (From: Alastair Houghton <email@hidden>)
 >Re: When do I need to override hash? (From: Jean-Daniel Dupas <email@hidden>)

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