Hi Gavin, ----- Mail original ----- > De: "Gavin Bierman" <gavin.bier...@oracle.com> > À: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "jan lahoda" <jan.lah...@oracle.com>, "amber-spec-experts" > <amber-spec-experts@openjdk.java.net> > Envoyé: Mardi 18 Février 2020 15:32:12 > Objet: Re: Pattern Matching for instanceof (Preview 2)
> [Just circling back to this, as I added a note about the grammar to the JEP > page…] > >> On 6 Feb 2020, at 20:38, Remi Forax <fo...@univ-mlv.fr> wrote: >> >> [moved to amber-spec] >> >> ----- Mail original ----- >>> De: "jan lahoda" <jan.lah...@oracle.com> >>> À: "amber-dev" <amber-...@openjdk.java.net> >>> Envoyé: Jeudi 6 Février 2020 21:18:52 >>> Objet: Pattern Matching for instanceof (Preview 2) >> >>> Hi, >>> >>> Thanks to Gavin, Brian and Alex, there is a new draft JEP for Pattern >>> Matching for instanceof (Preview 2): >>> https://bugs.openjdk.java.net/browse/JDK-8235186 >>> >>> Any feedback on the JEP is more than welcome! >>> >>> Thanks, >>> Jan >> >> so the difference with the previous preview is that deconstruction is added. > > That is correct. > >> >> I see two questions: >> - the grammar allows to mix var and non-var for a given reference type, i >> think >> that should only permitted if the non var is a deconstruction itself ? > > I don’t know what you mean here. There are two patterns, a type test pattern > and > a deconstruction pattern. In v2 we propose to support deconstruction patterns > over record types *only*. A deconstruction pattern looks like this: Point(var > a, var b), i.e. all the components are either (recursively) deconstruction > patterns, or `var` <identifier>, i.e. with no type needed. I added a note to > the JEP page pointing out that this is a starting point, and eventually we > will > support other patterns in the argument position, specifically <type> > <identifier>; hopefully in this release. Currently we don't support mixing var and non var in lambda parameters. So my question is: does this pattern Point(var x, int y) that mix a 'var' and an explicit type allowed or not ? > > >> - 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. > > Thanks, > Gavin regards, Rémi
