getPermittedSubclasses() on j.l.rClass returning an array of ClassDesc
Vicente Romero
vicente.romero at oracle.com
Sat Oct 24 21:40:58 UTC 2020
Hi,
The name of the method is still: permittedSubclasses
Vicente
On 10/24/20 7:35 AM, forax at univ-mlv.fr wrote:
> Ok nice,
> I suppose permittedSubclasses has been renamed to
> getPermittedSubclasses at the same time.
>
> Rémi
>
> ------------------------------------------------------------------------
>
> *De: *"Brian Goetz" <brian.goetz at oracle.com>
> *À: *"Gavin Bierman" <gavin.bierman at oracle.com>, "Remi Forax"
> <forax at univ-mlv.fr>
> *Cc: *"amber-spec-experts" <amber-spec-experts at openjdk.java.net>,
> "joe darcy" <joe.darcy at oracle.com>
> *Envoyé: *Vendredi 23 Octobre 2020 17:36:44
> *Objet: *Re: getPermittedSubclasses() on j.l.rClass returning an
> array of ClassDesc
>
> FTR: this was largely a "for consistency" decision, because
> nestmates does it the same way. (Which is to say, it was a
> deliberate suboptimal choice aimed at minimizing the number of API
> idioms that users of reflection had to deal with.)
>
> On 10/23/2020 11:27 AM, Gavin Bierman wrote:
>
> Just to follow this up; we have decided to change the signature of permittedSubclasses to the following:
>
> public Class<?>[] permittedSubclasses() {}
>
> Thanks!
> Gavin
>
> On 8 May 2020, at 23:53, Remi Forax<forax at univ-mlv.fr> wrote:
>
> The current draft of the reflection API for the sealed keyword adds a method getPermittedSubclasses() [1] to java.lang.Class.
>
> I'm not fully sure that returning an array of ClassDesc is the right choice here, mainly for two reasons,
>
> 1/ it's weird to return an array of ClassDesc when all others similar methods return an array of Class,
> I know why a ClassDesc might be "better" because it avoid the class loading,
> but it also means that now to fully understand java.lang.Class, people has to understand how java.lang.constant works.
> The java.lang.constant API was not designed for that, the first line of the overview of this package talks about descriptors, constant pool and indy, not something beginners should worry about.
>
> 2/ returning a symbolic view (ClassDesc) instead of a Class is *very* error prone from a user POV, to resolve a ClassDesc to a class, the user as to provide a Lookup
> and there is a good chance that users will pick the wrong ones. The number of people that understand classloading and how Lookup works is < 10,
> even experts struggle given the number of time the Lookup API as to be patched in recent years. Returning a ClassDesc in this context is like asking a child
> to read the serial number of a loaded gun.
> Perhaps a way to mitigate that is to provide the code a user should use to get the equivalent classes in the javadoc of getPermittedSubclasses().
>
> cheers,
> Rémi
>
> [1]https://bugs.openjdk.java.net/browse/JDK-8244556
>
>
>
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