Anton Vodonosov wrote:
22.01.2014, 20:11, "Robert P. Goldman" rpgoldman@sift.info:
Unfortunately, I don't see such a solution on the horizon: Pascal has demonstrated to my satisfaction that we cannot trap the *definition* of new OPERATION subclasses, only their instantiation. Faré has similarly ruled out deprecating OPERATION itself.
I don't think that preserving OPERATION semantics is really ruled out. Lets consider it a little bit more?
I am willing to do so. Faré is really the one who needs to judge this. See my remarks below.
Is it true that old ASDF:OPERATION is semantically equivalent to the new DOWNWARD-OPERATION? If yes, the proposal I made earlier looks appropriate:
OPERATION inherit from DOWNWARD-OPERATION COMPILE-OP inherit from OPERATION LOAD-OP inherit from OPERATION LOAD-SOURCE-OP inherit from OPERATION
I think if we were to do this, we would need to add a BASIC-OPERATION that would sit above the other operations and that would serve half of the purpose of the current OPERATION (providing a common root for all of the classes).
I think the danger is that existing methods that dispatch on OPERATION, intending to affect *all* operations would now be broken. They would have to be moved to BASIC-OPERATION. Repairing that might involve modifying more code than the current solution.
If we make so, these operations are backward compatible and at the same time fit the new ASDF 3 design.
The only relatively small issue we have is with TEST-OP. ASDF 3 wants TEST-OP to be just SELFWARD-OPERATION, while previous semantics of TEST-OP was inherited from old OPERATION, i.e. equal to the new DOWNWARD-OPERATION.
I think it is a small issue and there are number of ways solving it:
- Make TEST-OP just SELFWARD-OPERATION, thus breaking compatibility, but only for the code depending which rely on TEST-OP to have downward semantics. It is a smaller compatibility break than breaking any OPERATION-extending code. Probably there is no code at all which relies on TEST-OP being downward.
I believe that to be correct. The only examples of TEST-OP that I know of involves a test system, with files that define tests according to some library, and a PERFORM method on TEST-OP at the system level that invokes some function in the test framework (e.g., fiveam:run!) to run the tests that the component files have defined.
When I say "I believe that to be correct," credit is due to Faré for thinking this true and convincing me that SELFWARD is correct and DOWNWARD is not correct.
- Accept that new TEST-OP is a DOWNWARD-OPERATION - maybe it compromises new ASDF 3 design a bit, but we are fully backward compatible.
I believe that the way the existing code for TEST-OP was made to work in the presence of downward dependency propagation was to define no-op methods something like this:
(defmethod perform ((op test-op) c) (values))
so that when dependencies were propagated down to individual files, they would do nothing.
Your solution 2 would preserve these.
- Do with TEST-OP the same I propose for OPERATION - make it a backward compatibility stub, a DOWNWARD-OPERATION, but also introduce new ASDF3:TEST-OP which is a SELFWARD-OPERATION
I would prefer, in order, your solution 1, 2, 3.