[cdr-discuss] AEQUALIS and COMPARE

[Marco Antoniotti]

On Feb 15, 2011, at 14:36 , Attila Lendvai wrote:

>> - The idea that COMPARE returns symbols also seems weird to me. Wouldn't it be better to return numbers (-1, 0, +1 or NIL)? Can't immediately tell why, though.
> 
> 
> you need to return well-known identities that communicate the result.
> -1,0,+1 are the easy way for well-known identities in C. in CL,
> symbols provide a much nicer framework to deal with well-known
> identities IMO.

That was the thinking.

>> - Shouldn't there also be a hash-code generic function that can be specialized alongside AEQUALIS? This also exists in Java and C#, and could make this immediately more useful (and would be much harder to add later as an afterthought). Many CL implementation add an :sxhash option to make-hash-table, where such a hash-code function could be used.
> 
> 
> a big +1 for the above.


You should but:

As in Java (and FWIU in C#) there are no "easy" ways (for an appropriate definition of "easy") to enforce the protocol.
What would be the default?  Something like

		(defmethod hash-code ((x t)) (sxhash x))


If you think so, I can add it to the doc.  Always with the caveat that there is no way to enforce the relationship between equality and hashing.

Marco

PS.  Yeah.  AEQUALIS is very Latin :)  Any synonym?  I will just vote against EGAL, which I really don't like :)








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Marco Antoniotti


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