Notes from the discussion: > On Jul 15, 2020, at 12:01 AM, Dan Smith <daniel.sm...@oracle.com> wrote: > > The next EG Zoom meeting is tomorrow, 4pm UTC (9am PDT, 12pm EDT). > > Recent threads to discuss: > > - "JEP draft: Identity Warnings for Inline Class Candidates": I drafted a JEP > that lists candidates for inline class migration and describes the compiler > and runtime warnings needed to prepare for their migration
Remi wondered whether changing the semantics of '==' for wrapper classes will be a problem. Answer: constructors will be deprecated; for the small integers (-128 to 127?) produced by 'valueOf', == will have the same behavior; for the large integers produced by 'valueOf', behavior of == is currently unspecified, so we're fine to change behavior. There's a consensus that we should probably track the inline class candidates (or maybe all value-based classes?) with an annotation. > > - "Revisiting default values": I described use cases for different treatments > of inline types' default values, and then summarized various strategies for > supporting some of the nontrivial use cases General agreement that the "Bucket #3" group (classes without a natural default) is what we should focus on, not the "Bucket #2" group (classes that want a nontrivial default). We talked through various "Bucket #3" approaches. The preferred approaches seem to be: - Guards on member access, either compiler-generated or JVM-enforced. Fields and default methods require special attention. (May involve making the invalid default equivalent to "null", but there are complexity concerns.) - Tracking uninitialized fields/arrays in the JVM. There's concern about performance of array reads, best optimization might be adding a boolean "isInitialized" flag to each flattened value. There's also concern about tearing producing unexpected default values in corner cases, possibly mitigated with our story for atomicity. - Bucket #3 classes must be reference-default, and fields/arrays of their inline type are illegal outside of the declaring class. The declaring class can provide a flat array factory if it wants to. (A new idea from Tobi, he'll write it up for the thread.)
