Re: [Caml-list] modifying hash tables

["Christopher L Conway" <cconway@cs.nyu.edu>]

Assuming that your question is "is it OK to modify a Hashtbl while you
iterate over it?" and assuming that the answer is "maybe, but maybe
not" and assuming that I am looking for a way to avoid doing real
work, you might try the following:

(Hashtbl.fold
   (fun key data f ->
     (fun ht -> Hashtable.replace ht key (data+1); f ht))
   ht
   (fun _ -> ()))
  ht

Chris

On 7/18/07, Sam Steingold <sds@gnu.org> wrote:
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> I want to modify the _current_ datum in Hashtable.iter, e.g., increment
> a count. Is this code valid?
> Hashtable.iter ht ~f:(fun ~key ~data ->
>   Hashtable.replace ht ~key ~data:(data+1))
> (it appears to work, but I was told that "it is not guaranteed to work",
> i.e., the documentation does not promise that).
> If the above code is wrong, what is TRT?
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