Re: [Caml-list] Default values for structures (feature request)

[Sven Luther <sven.luther@wanadoo.fr>]

On Wed, Jun 02, 2004 at 09:56:55PM +0900, Jacques GARRIGUE wrote:
> From: Richard Jones <rich@annexia.org>
> 
> > Could have a syntax for default values for structures?  Something
> > like:
> > 
> > type t = { field1 : int = 0;
> >            field2 : string;  (* no default *)
> >          }
> 
> The difficulty should be apparent in your example: this supposes
> writing values in interfaces, which would be a major (huge) change in
> language design...
> 
> Note that labeled arguments let you do that.
> 
> let new_t ?(field1 = 0) ~field2 () = {field1=field1; field2=field2}
> 
> > The reason for having default fields is so that I can export struct-
> > ures from my module interface, but be able to add fields with default
> > values later without breaking dependent code.  (But in some circum-
> > stances I would deliberately add fields without default values in
> > order to break code).
> 
> This is the point with optional/labeled arguments.
> Jacques Garrigue

Well, what about adding a syntaxic wrapper over those to let you
automatically do it using a syntax similar to what Richard Jones
proposed ?

Friendly,

Sven luther

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