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Hash clash in polymorphic variants
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Date: -- (:)
From: David Allsopp <dra-news@m...>
Subject: RE: [Caml-list] Hash clash in polymorphic variants
Jon Harrop wrote:
> On Thursday 10 January 2008 20:35:34 Eric Cooper wrote:
> > On Thu, Jan 10, 2008 at 05:09:13PM +0000, Jon Harrop wrote:
> > > ISTR advice that constructors sharing the first few characters should
> > > be avoided in order to reduce the likelihood of clashing hash values
> > > for polymorphic variants. Is that right?
> >
> > I don't think it's worth worrying about.
> >
> > I wrote a program a while ago to look into this.  I never saw any
> > "human-sensible" collisions (between two identifiers that a person
> > might have chosen). And if you're producing gensyms in a program, you
> > can just check ahead of time.
>
> I'm interested in automatically translating the GL_* enum from OpenGL into

> polymorphic variants. So although it is generated code I have little
> control over it, e.g. I cannot change the translation as OpenGL gets
> extended because 
> code will already be using the existing names.
>
> Still, maybe I'm over-reacting. ;-)

I presume you're worried about the bindings clashing internally rather than
someone who uses the library happening to use a variant that clashes?

You can do something about it - when you're generating your bindings, you
can use the hash_variant() C function to detect the collisions yourself. If
you detect one, you can either issue *your own* warning while generating the
bindings allowing you to specify specific renaming for the program
generating your bindings or you could append digits to the names until the
collisions disappear (which is likely, though not guaranteed, to happen
quickly).

It's slightly ugly, but then the possibility of collisions in the first
place is IMHO ugly too!


David