but can I compatibly turn a class type into a record type? It's
potentially a source-compatible change (make the state description
match the class's ctor), but binary-compatible?
Yes. You can transform
class Point {
final int x, y;
public Point(int x, int y) { this.x = x; this.y = y; }
public int x() { return x; }
public int y() { return y; }
// state-based equals and hashCode
// more methods
}
into
record Point(int x, int y) {
// more methods
}
and this will be source- and binary-compatible.
Similarly, if a record type is chafing at the restrictions of "state
only!", then can I (source|binary)-compatibly turn it into a class type?
Yes, mostly. Records do currently have one aspect that is not *yet*
denotable by ordinary classes; the pattern match extractor. Until
ordinary classes can declare one, existing records whose clients use
pattern matching can't be migrated.
