----- Mail original -----
> De: "Chris Hegarty" <[email protected]>
> À: "Vicente Romero" <[email protected]>
> Cc: "Remi Forax" <[email protected]>, "amber-spec-experts"
> <[email protected]>
> Envoyé: Mardi 27 Octobre 2020 12:45:13
> Objet: Re: getPermittedSubclasses() on j.l.rClass returning an array of
> ClassDesc
> While I agree with all comments in this thread so far, I have one additional
> comment relating to the type parameter.
>
> Since the set of permitted classes must be subclasses of T, should the
> declaration be:
>
> public Class<? extends T>[] getPermittedSubclasses() { .. }
Hi Chris,
in theory yes,
in practice, an array of parametrized types is usually unsafe, in this peculiar
case, it's always unsafe because you can write
Class<? extends Itf>[] array = Itf.class.getPermittedSubclasses();
Object[] array2 = array;
array2[0] = Object.class;
Itf itf = array[0].newInstance(); // CCE, the compiler insert a cast to Itf
and Object doesn't implement Itf
>
>
> -Chris.
Rémi
>
>
>> On 26 Oct 2020, at 14:15, Vicente Romero <[email protected]> wrote:
>>
>> Hi Remi,
>>
>> I will update the name, adding the `get` back,
>>
>> Thanks,
>> Vicente
>>
>> On 10/24/20 6:32 PM, [email protected] 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" <[email protected]>
>>> À: "Remi Forax" <[email protected]>, "Brian Goetz" <[email protected]>,
>>> "Gavin Bierman" <[email protected]>
>>> Cc: "amber-spec-experts" <[email protected]>, "joe darcy"
>>> <[email protected]>
>>> 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, [email protected] wrote:
>>> Ok nice,
>>> I suppose permittedSubclasses has been renamed to getPermittedSubclasses at
>>> the
>>> same time.
>>>
>>> Rémi
>>>
>>> De: "Brian Goetz" <[email protected]>
>>> À: "Gavin Bierman" <[email protected]>, "Remi Forax"
>>> <[email protected]>
>>> Cc: "amber-spec-experts" <[email protected]>, "joe darcy"
>>> <[email protected]>
>>> 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 <[email protected]>
>>> 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
>>>
>>>
>>>
>>>
