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Date: Fri, 4 May 2012 13:38:48 +0000 (UTC)
From: "Gilles (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (MATH-786) "hashCode" in "Pair" class
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    [ https://issues.apache.org/jira/browse/MATH-786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13268358#comment-13268358 ] 

Gilles commented on MATH-786:
-----------------------------

I already notice a problem with this proposal: the elements of the pair might well be mutable, and since we store references, not copies, of the objects passed to the constructor, we cannot ensure that "equals" will stay consistent with the cached "hashCode"!

Does someone see a way to make "Pair" truly immutable?

                
> "hashCode" in "Pair" class
> --------------------------
>
>                 Key: MATH-786
>                 URL: https://issues.apache.org/jira/browse/MATH-786
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.0
>            Reporter: Gilles
>            Assignee: Gilles
>            Priority: Trivial
>             Fix For: 3.1
>
>
> Since "Pair" is supposed to be an immutable class, couldn't we cache the "hashCode" value at construction? That would supposedly make it more efficient when used in maps.

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