getPermittedSubclasses() on j.l.rClass returning an array of ClassDesc

Vicente Romero vicente.romero at
Mon Oct 26 14:15:46 UTC 2020

Hi Remi,

I will update the name, adding the `get` back,


On 10/24/20 6:32 PM, forax at wrote:
> Hi Vicente,
> the 'get' was removed because the method was not returning Class 
> objects, now that permittedSubclasses behave like the other methods of 
> java.lang.Class,
> the name should be changed back to "get..." to reflect that.
> Rémi
> ------------------------------------------------------------------------
>     *De: *"Vicente Romero" <vicente.romero at>
>     *À: *"Remi Forax" <forax at>, "Brian Goetz"
>     <brian.goetz at>, "Gavin Bierman" <gavin.bierman at>
>     *Cc: *"amber-spec-experts" <amber-spec-experts at>,
>     "joe darcy" <joe.darcy at>
>     *Envoyé: *Samedi 24 Octobre 2020 23:40:58
>     *Objet: *Re: getPermittedSubclasses() on j.l.rClass returning an
>     array of ClassDesc
>     Hi,
>     The name of the method is still: permittedSubclasses
>     Vicente
>     On 10/24/20 7:35 AM, forax at wrote:
>         Ok nice,
>         I suppose permittedSubclasses has been renamed to
>         getPermittedSubclasses at the same time.
>         Rémi
>         ------------------------------------------------------------------------
>             *De: *"Brian Goetz" <brian.goetz at>
>             *À: *"Gavin Bierman" <gavin.bierman at>, "Remi
>             Forax" <forax at>
>             *Cc: *"amber-spec-experts"
>             <amber-spec-experts at>, "joe darcy"
>             <joe.darcy at>
>             *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>  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]

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