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Date: Tue, 3 Aug 2004 13:02:44 +0100
To: caml-list@inria.fr
Subject: [Caml-list] Functors and classes
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From: Richard Jones <rich@annexia.org>
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I'm trying to replace the current mod_caml approach to pooling
database handles with a functorized one.  However there seems to be
some problem with the way functors and classes interact.

I have a hierarchy of classes:

      Dbi.connection
           |
           ^
           |
   +----------- - - - etc.
   |
 Dbi_postgres.connection

I'd like to create a pool of "postgres connections" using something
like:

  module MyPool = Apache.DbiPool (Dbi_postgres)

So far, the apache.mli looks like below.  It doesn't compile because:

  Unbound type constructor DbiConnection.connection

at the last line.

Is this sort of thing even possible?

Rich.

------------------------------------------------------- apache.mli ---------
module type DbiConnection = sig

  class connection : ?host:string -> ?port:string ->
			      ?user:string -> ?password:string -> string ->
  object
    method close : unit -> unit
    method closed : bool
    method ping : unit -> bool
    method rollback : unit -> unit
  end

end

module type DbiPoolT = sig

  type connection

  val get : Request.t -> ?host:string -> ?port:string ->
    ?user:string -> ?password:string -> string -> connection
end

module DbiPool (Dbi : DbiConnection) : DbiPoolT
  with type connection = DbiConnection.connection
----------------------------------------------------------------------

-- 
Richard Jones. http://www.annexia.org/ http://www.j-london.com/
Merjis Ltd. http://www.merjis.com/ - improving website return on investment
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