Re: [Caml-list] Record field disambiguation in 4.01

[Yaron Minsky <yminsky@janestreet.com>]

On Mon, Mar 11, 2013 at 7:52 AM, Alain Frisch <alain@frisch.fr> wrote:
> On 03/10/2013 12:39 AM, Yaron Minsky wrote:
>>
>> Also, I'm wondering if anyone has thoughts as to how much code this
>> change will break?  The answer might be "quite a lot", and it might
>> nonetheless be worth it.  But I'm curious what people's thoughts are.
>
>
> As Jacques said, this is only a warning, which is turned off by default.  I
> expect that all the "unused stuff" warnings also broke most code bases
> around which are compiled with "-w +A -warn-error A".  I'm sure you are not
> suggesting that new warnings should never be triggered on code which used to
> be well-typed by a previous version of the compiler...

That is entirely sensible.  I normally run with all warnings on, minus
a handful of explicit ones I don't want.  That normally works well
(since most new errors are in fact helpful!)

> The warning tells you something useful: with that record type declaration,
> the reference to field "y" becomes ambiguous, which means in particular that
> (i) your code might become fragile w.r.t. reordering of type declarations,
> (ii) the code might become harder to read (the reader might expect that
> field "y" is typically related to a different record type in your code
> base).  Of course, a more explicit warning message, as you suggest, would be
> even better.

Agreed.

> During the discussion on type-based disambiguation, Mark Shinwell commented
> that most record types in JS code base are defined in nested modules (and
> often exposed only through builder functions) to avoid label clashes.  Is
> your example an instance where this is not the case?

It is.  If I'd turned the warning off, would it have in fact picked
the more recent definition?

y

>
> Alain
>
>
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