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hashcode and Map (non mutable case) [message #942521]

Sat, 13 October 2012 12:01

David Michonneau
Messages: 81
Registered: July 2009

Member

I'm coming back with yet another question about using EObject as keys in Maps. I have read previous posts, javadoc, etc... So I know it is not supported to override hashcode()/equals(). But, this remains a major annoyance, and I agree that it is a bad idea to use mutable objects as keys in HashMaps.

The point is that I use EMF to generate all my model classes, mutable and non-mutable ones. It doesn't seem there is any good reason to prevent the mutable ones to be keys in maps (and especially EMF generated maps, after all those are EMF specialized map classes).

So here is my question: I model a non-mutable class, let's call it Identifier, with two attributes:
- String name
- String path

The two attributes must be set at the construction of Identifier, so I only create instances through a new factory method createIdentifier(name, path). Nobody ever calls setter (or assume I remove setter methods).

Now, given those hypotheses, can I override hashcode/equals to put this Identifier object into an EMap (modeled in the ecore)? Will it cause any problem? If so, can we envision an enhancement to model special immutable objects that will have a generated hashcode/equals (by default hashcode of attributes), that could be overriden? I guess all EMF code (lists, copier,...) would be able to detect those immutable objects, and process them accordingly. Moreover, it would generate smart factory methods for those with all its attributes as arguments.

Thanks,

David

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[Message index]

		hashcode and Map (non mutable case) By: David Michonneau on Sat, 13 October 2012 12:01
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: David Michonneau on Sun, 14 October 2012 04:50
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 05:39
		Re: hashcode and Map (non mutable case) By: David Michonneau on Sun, 14 October 2012 11:39
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 12:37
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Merks on Sun, 14 October 2012 00:58
		Re: hashcode and Map (non mutable case) By: Ed Willink on Sun, 14 October 2012 03:10

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