Major changes:
There are two new operators e in e and e in super. They perform the same role as std.objectHasAll, i.e. they allow you to discover whether a field exists, except that std.objectHasAll(super, e) cannot be expressed since super is not allowed in isolation. The semantics of e in super are quite interesting because it returns false even if there is no super object.
There is a subtle change to the semantics of +: and related field definitions. Previously if the super-object did not have the field f then f +: e was an error. Now, it succeeds in that case yielding f: e. This extends recursively, so { } + { f+: { x +: { y: 1 } } } yields { f: { x: { y: 1 } } }, and in fact the left hand side { } is not even needed. You can evaluate a mixin like { f+: { x +: { y: 1 } } } without even applying it to anything. This is a backwards compatible change because it only affects the behavior of programs that used to fail.
Minor other changes in this release:
- Addition of std.prune
- Fix of uninitialized value (undefined behavior) in desugarer.