Updated patterns-in-switch doc

Brian Goetz brian.goetz at oracle.com
Sun Sep 13 22:23:33 UTC 2020

I find these arguments not-remotely-compelling. Variable declarations 
should look like declarations; it is highly error-prone to have the mere 
mention of a name cause it to spring into being.  I see no value, and 
much anti-value, in having `Point(x)` introduce a new variable x.

So, no.  I think that would be a very bad idea.

On 9/13/2020 3:10 PM, forax at univ-mlv.fr wrote:
> ------------------------------------------------------------------------
>     *De: *"Brian Goetz" <brian.goetz at oracle.com>
>     *À: *"Remi Forax" <forax at univ-mlv.fr>
>     *Cc: *"amber-spec-experts" <amber-spec-experts at openjdk.java.net>
>     *Envoyé: *Dimanche 13 Septembre 2020 20:34:54
>     *Objet: *Re: Updated patterns-in-switch doc
>             I don’t quite get the leap from “no constant patterns” to
>             changing the syntax of deconstruction patterns, but in any
>             case, we definitely don’t want this (and in fact, for the
>             same reasons cited in the section on constant patterns,
>             and others.)
>         if case Point(x, y) can not mean instanceof Point p where p.x
>         == x && p.y == y, then case Point(x, y) can have the same
>         meaning has a lambda (x, y), introducing two fresh variables x
>         and y.
>     If you're making the claim that "It would not be disastrously
>     inconsistent for it to work that way", I agree.  But I think it
>     would still be quite foolish of us to go that way anyway.  The
>     benefit is tiny (a few fewer characters typed) at a very
>     considerable cost -- reduced readability, and potential ambiguities.
> The main issue i see with using var is that when you have nested 
> patterns, "var" starts to becomes noise because you start to have 
> several of them, so it makes the nesting less obvious.
> For me, var is good the first times to see how pattern matching works, 
> it's very similar how as a beginner you are prefixing everything with 
> "this" but after some times, it falls into the noise category,
> that why i'm not proposing to not allow "var" but to allow to not use 
> "var".
> Again, this is very similar to the things we were discussing during 
> the conception of lambdas, should we try to protect them with a lot of 
> syntax to say, this is the new thing or should we try to make the 
> syntax simpler with the risk of people not understanding it.
> Rémi

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