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

Remi Forax forax at
Fri May 8 22:53:03 UTC 2020

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().



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