From: Clifford Heath <no@...>
Date: 2011-04-30T16:45:24+09:00
Subject: Re: Hash Surprises with Fixnum, #hash, and #eql?

On 04/27/11 15:23, Charles Oliver Nutter wrote:
> On Wed, Apr 20, 2011 at 9:53 PM, Clifford Heath<no@spam.please.net>  wrote:
>> I'm not. I'm expecting that JRuby would detect that a core Fixnum
>> method has been monkey-patched, and set a global variable.
>> ...
> Well, it has to get the value from somewhere. ... it's two field
> dereferences and one (inlined) virtual method invocation

Ouch. No wonder it hurts. I hadn't looked into the internals of JRuby,
but I assumed that you had some native C (JNI or whatever) in there,
which could make this feasible.

I can totally understand you not wanting any native extensions though!

It seems that a collection of such flags at known offsets inside a
singleton instance could make this a lot quicker. There's a finite
need for such things, so it's not as though it would pervade all of
the interpreter.

Your argument (from a previous response) that cross-thread effects of
monkey-patching was "somewhat undefined" was my thinking also, but
contrary to John's accusation, thought it could be (mostly?) hidden
under the existing synchronisation around method definition.

> In general we have followed the path of matching MRI in such cases,
> except when there's a very strong argument not to do so. If you can
> convince Ruby core, or if you think you have a strong enough case for
> deviating from MRI's behavior, go ahead and file the bug and we can
> continue exploring it there.

I think the argument that "folk don't do it, therefore they wouldn't"
isn't a strong one. Look for example at Rail's HashWithIndifferentAccess,
which makes string and symbol keys interchangeable. I merely want to
do the same thing with Fixnums and Floats.

If you can't make it quicker (than you outlined), best to drop it I
guess. I've mostly worked around the need for my current library.

Clifford Heath.