On Feb 22, 2019, at 6:57 PM, John Rose <john.r.r...@oracle.com> wrote: > > On Feb 22, 2019, at 11:42 AM, Kevin Bourrillion <kev...@google.com> wrote: >> >> I think we should make users write `equals` to test value types. If they >> write `==`, they are indicating a special situation where they need identity >> semantics, which don't make sense for value types, and that should be an >> error. > > This sounds like a proposal for the future, but as Brian points > out it is also a constraint on large amounts of generic code > that has already been written. > > Let's make the best of op==; it's in our past and the future > of comparison logic in Java is too tightly coupled with the past. > > — John
P.S. Also, in exactly-typed code, the substitutability test will *often* be exactly what the user wants. The default implementation of ValObject.equals will use that test, and users will surely opt to inherit that rather than write a local equals method that does the same. (Not always, of course; there are value types and object types where the default equals method doesn't DTRT. But often, for cases like small numerics and tuples.) In that value class, requiring the user to call x.equals(y) instead of writing the known exact equivalent x==y feels like somebody's code style policy, rather than a useful discipline.
