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Message-ID: <4B682A63.8010101@frisch.fr>
Date: Tue, 02 Feb 2010 14:36:35 +0100
From: Alain Frisch <alain@frisch.fr>
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To: =?UTF-8?B?RGFuaWVsIELDvG56bGk=?= <daniel.buenzli@erratique.ch>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Thread safe heterogenous property lists (dictionaries)
References: <91a3da521002020512v758849f0mdac3538abac44161@mail.gmail.com>
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X-Spam: no; 0.00; frisch:01 frisch:01 logarithmic:01 fwiw:01 syntax:01 ocaml's:01 struct:01 wrote:01 exception:01 caml-list:01 alain:01 alain:01 ids:03 ids:03 module:03 

On 02/02/2010 14:12, Daniel Bünzli wrote:
> The second one uses Maps for logarithmic time lookups. Operations on
> dictionaries are thread safe. However key creation is not because
> unique ids need to be generated for them.

FWIW, a thread-safe way to generate fresh ids is:

let fresh_id () = Oo.id (object end)


Also, the "perfect" solution you are referring to becomes in the syntax 
of OCaml's trunk:

let embed () (type s) =
   let module M = struct exception E of s end in
   (fun x -> M.E x), (function M.E x -> Some x | _ -> None)


-- Alain