Pattern Matching for instanceof (Preview 2)

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Gavin Bierman" <gavin.bierman at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "jan lahoda" <jan.lahoda at oracle.com>, "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
> Envoyé: Mardi 18 Février 2020 17:35:03
> Objet: Re: Pattern Matching for instanceof (Preview 2)

>> On 18 Feb 2020, at 15:04, forax at univ-mlv.fr wrote:
>> 
>> Hi Gavin,
>> 
>> ----- Mail original -----
>>> De: "Gavin Bierman" <gavin.bierman at oracle.com>
>>> À: "Remi Forax" <forax at univ-mlv.fr>
>>> Cc: "jan lahoda" <jan.lahoda at oracle.com>, "amber-spec-experts"
>>> <amber-spec-experts at openjdk.java.net>
>>> Envoyé: Mardi 18 Février 2020 15:32:12
>>> Objet: Re: Pattern Matching for instanceof (Preview 2)
>> 
>>> 
>>>> - must the identifier of a pattern argument be the same name as the
>>>> corresponding record component ?
>>>> To be coherent with the fact that constructors requires the same names.
>>> 
>>> Absolutely not! Note this does mean that you can write confusing code:
>>> 
>>> record Point(int x, int y) { }
>>> 
>>> if (o instanceof Point(var y, var x)) {
>>> … // y refers to x component, y refers to x component
>>> }
>>> 
>>> (I’ll get my coat…)
>> 
>> yes, that's why i ask, it leads to very confusing code, some languages don't
>> allow this kind of code,
>> by example destructuring in JavaScript as a special syntax if you want to use
>> different names.
> 
> I appreciate this, but requiring you to use the record component name is not
> very friendly if you have repeated nested patterns, e.g.
> 
> if (o instanceof Line(Point(int x, int y), Point(int x, int y))) // Error two
> occurrences of x and y!
> { …}
> 
> The only way around that would be to have explicit renaming operators, which is
> pretty ugly.


yes, very good point.

> 
> Gavin

Rémi