On 2 October 2015 at 13:12, Auke Booij <a...@tulcod.com> wrote: > The wayland protocol currently does not specify the enum attribute, > and I see no way how to write an API whose entire purpose is to > *break* when you erroneously mix up enum attribute data, without > breaking API as this data is added.
Actually, for my particular scenario, I just thought of a very elegant solution that would introduce no new compatibility issues. With this solution, *more* code would compile *with* the right enum attributes than *without*. So we would have the best of both worlds: the type safety that modern languages want, without new compatibility issues to keep track of. (If anyone is interested in the technicalities behind this, contact me. But it is a solution that is rather specific to Haskell. Essentially, it would work by, rather than passing enum values as ints until we have a proper data type for them, we would pass each field as a different data type, until we know that two enum fields should have been the same type. In haskell, this can be done in a backwards-compatible way.) Maybe a solution can be found in more languages, and we can make the compatibility, that e.g. Pekka is looking for, a requirement for bindings, rather than make compatibility a requirement for the protocol writers. So something along these lines would be in the specification: [start] The enum and bitfield attributes are in principle for documentation purposes only. The enum and bitfield attributes may also be used by bindings, but only in such a way that code written prior to the specification of these attributes still works after their specification. In other words, specifying an attribute for an argument, that previously did not have it, should not break API. [end] Obviously C is not rich enough to do this in an elegant way. (Maybe it's possible in C++ with some template magic?) But it definitely solves the "backwards compatibility" debate, since, while anyone is free to ignore this bit in the specification, solutions might sometimes be possible, and it guards the entire C world from issues in the non-C bindings. _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel
