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Date: Mon, 07 Jun 2010 21:07:19 +0300
From: =?ISO-8859-1?Q?T=F6r=F6k_Edwin?= <edwintorok@gmail.com>
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To: caml-list@yquem.inria.fr
Subject: Converting variants with only constant constructors to integers
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X-Spam: no; 0.00; variants:01 constructors:01 integers:01 constructors:01 ocaml:01 hashtbl:01 hash:01 edwin:98 integer:01 integer:01 assert:01 functions:01 constructor:01 int:01 int:01 

Hi,

What is the recommended way to convert a variant that has only constant
constructors to an integer? (an integer that is unique for each constant
constructor, preferably sequential in the order in which they are declared).

I found the following two possibilities, but I am not sure if these are
guaranteed to return the same results for future versions of OCaml or not:

let int_of_constant_variant a : int = Hashtbl.hash a;;
let int_of_constant_variant a : int =
 let r = Obj.repr a in
  assert (Obj.is_int r);
  (Obj.magic r : int);;

for 'type t = A | C | B', both of these functions return 0,1, and 2 for
A,C, and B respectively.

Best regards,
--Edwin