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Date: Thu, 12 Apr 2012 19:21:09 +0200
From: Alain Frisch <alain@frisch.fr>
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To: Leo P White <lpw25@cam.ac.uk>
CC: Gabriel Scherer <gabriel.scherer@gmail.com>, caml <caml-list@inria.fr>
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Subject: Re: [Caml-list] [ANN] ocamlopen 1.0.2

On 04/12/2012 07:07 PM, Leo P White wrote:
> Just like exceptions, they are represented as constructors whose first
> field points to an address that is allocated by the extension definition
> to represent that extension. They have a special tag value so that
> structural equality knows to compare the first fields by address. Note
> that this is exactly what is required to fix the bug with structural
> equality on exceptions (4765).

Do we really need a new special tag?  Why not use Object_tag and 
represent slots as blocks of size 2 (constructor name + unique integer 
as the second field)?  This would have the following consequences (which 
are the expected ones):

  - The generic equality function compares the unique ids.

  - The generic hash function returns the unique id.

  - The generic unmarshaling function allocates a fresh id when 
umarshaling such a block.


Alain