I don't think so. A compact constructor (or require initializer, as
you propose) could be not the only constructor. An instance
initializer is convenient because it's added to every constructor,
regardless of whether it's compact or not. So the new thing doesn't
supersede the instance initializer and I see no good reason to
explicitly disable it.
Vicente offered another reason why we might want to prohibit the
instance initializer, if only out of expediency; it complicates the
analysis of which fields are DA on all paths through the constructor
(and therefore, do not need to be automatically initialized.) If you
have a record:
record Foo(int i) {
{ this.i = 0; }
}
then the canonical constructor has to see that `i` is always initialized
by the static init, and therefore should be not initialized. Worse, if
we have:
record Foo(int i) {
{ if (tuesday) this.i = 0; }
}
then we have to issue a compilation error, since we have fields that are
neither DA nor DU at the end of the initializer.
None of this is impossible to do, of course; it's just not clear whether
it's worth it, given the limited utility of instance initializers in
records (because we've already banned instance fields.)
