RFR: universal type variables: initial prototype [v3]

[Rémi Forax]

On Wed, 11 Aug 2021 16:23:34 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> I double checked with Brian yesterday - he confirmed that both `T` and `T.ref` should not support identity operation (well, given warning when attempting to).
>
> ok, thanks for double checking, will fix this

T.ref still support == null, but it's a corner case

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PR: https://git.openjdk.java.net/valhalla/pull/521