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https://issues.apache.org/jira/browse/THRIFT-68?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12610278#action_12610278
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Todd Lipcon commented on THRIFT-68:
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I disagree here. The default generator *does* generate a proper .equals()
method which determines object value equality. The default implementation of
Object.hashCode() returns a value based on the object reference, not the object
value. Therefore, if we were to not implement hashCode() we would break the
contract that a.hashCode() == b.hashCode() if a.equals(b).
Always returning 0 is not terribly smart, since everything will hash to the
same bucket and give hash-based containers O(n) lookup performance, but it's
better than nothing, which would give them incorrect semantics.
> Generated types define a hashcode method that always returns 0
> --------------------------------------------------------------
>
> Key: THRIFT-68
> URL: https://issues.apache.org/jira/browse/THRIFT-68
> Project: Thrift
> Issue Type: Bug
> Components: Compiler (Java), Library (Java)
> Reporter: Bryan Duxbury
> Priority: Minor
>
> When not using the "hashcode" option with the Java generator, the hashCode
> method that is created always returns 0, regardless of the type or instance.
> This makes it completely impossible to use as a hash key (or in a hash set).
> This is particularly curious because the default Java Object#hashCode method
> returns a reasonably unique hashcode per object instance. Thus, the hashCode
> method on generated types is actually explicitly worse than default.
> I think at the very least we should remove the hashCode method declaration
> and let the superclass method take care of it. At best, I think it would make
> sense for us to write a simple real hashCode method that produced something
> reasonably unique, if not perfect. If you need super hashCodes, then you can
> use the "hashcode" option and just plan on using the external jar that it
> requires.
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