Deprecations for 3.0

[Peter Lobsinger]

Hi,

As noted this week on #ps, some of the goals we have for 3.0 require
that some existing functionality be deprecated before they can be
complete. The 2.9 supported release next month is the last chance to
get these deprecations in time to allow our 3.0 goals to be met, so we
need to start thinking about this now.

Hereare  some of the milestones for 3.0 and possible deprecation concerns:

GC:
  * Generational:
     * requires barriers to handle bookkeeping at reference creation
     * existing object attribute access barriers are:
       (a) unwieldy and therefore not used consistently
       (b) insufficient to support more complicated uses. a good
example is PMC aggregates.
     * we need a more general way of indicating reference creation and
we need to require that users use it
  * Copying:
     * object motion might require explicit pinning of objects with
references on the C stack (currently handled magically by stack
walking)

lvalue semantics:
  * not sure if we have a concrete plan on this. do we have any
planned/desired changes in this area that would be blocked by
deprecation?

native typed lexicals:
 * this is purely adding functionality
 * likely doesn't need deprecations.

concurrency:
  * not really sure where we are or what lies ahead here. anyone care
to forecast?

pirc:
  * incompatibilities with imcc (if any) likely need deprecations
  * stalled, so these incompatibilities are unknown at the moment

Comments? Are there other tasks slated for 3.0 that we can try to
guess the deprecations for? Are there other issues related to these
tasks?

Sources:
  * https://spreadsheets.google.com/ccc?key=0Ahm1zTZwW0VHdFVPSW1BemVEZU82RkFrZDZ5cTdtYXc&hl=en
  * http://trac.parrot.org/parrot/report/14