Re: [Caml-list] Stability of order between polymorphic variants

[Francois Berenger <berenger@riken.jp>]

On 09/05/2013 11:11 AM, Anthony Tavener wrote:
> Addendum: On a 32b arch, those names will wrap.

Why not write a to_int for your type
and then a specialized comparator using it?

> On Wed, Sep 4, 2013 at 8:06 PM, Anthony Tavener
> <anthony.tavener@gmail.com <mailto:anthony.tavener@gmail.com>> wrote:
>
>     I haven't looked at how the compare happens for polyvariants, but I
>     assume it's going to treat them as integers. And the integer value
>     of the polymorphic variants is a simple hashing-type function
>     (byterun/hash.c: caml_hash_variant). A multiplication by 223 is
>     involved for each character of the variant name, so with a long
>     enough name, compared to the integer size, you'll get wraparound.
>     The short names you have there are okay.
>
>     I'd be uncomfortable relying on this ordering, but I can imagine it
>     would make some things a lot simpler...
>
>
>
>     On Wed, Sep 4, 2013 at 6:17 PM, Daniel Bünzli
>     <daniel.buenzli@erratique.ch <mailto:daniel.buenzli@erratique.ch>>
>     wrote:
>
>         Hello,
>
>         I have this type
>
>            type weight = [ `W100 | `W200 | `W300 | `W400 | `W500 | `W600
>         | `W700 | `W800 | `W900 ]
>
>         In the current compiler it has the property that `Wx00 < `Wy00
>         if x < y.
>
>         The question is, is the order between polymorphic variants an
>         invariant provided by the compiler or is it subject to change ?
>
>         Best,
>
>         Daniel
>
>
>
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