On 25 Jan 2014, at 23:29, Faré <fah...@gmail.com> wrote: >> OK, will do. I will try to get all of the new operations written up, >> but I don't believe I will have time until after the 31st (conference >> deadlines, and end of contract dates mean that the ASDF manual has to >> wait...). >> > Take your time. We're all impatient about it. > >> I do not yet the proposal. How can OPERATION keep the old semantics and >> still be the root? There are 11 direct subclasses of OPERATION now, and >> some fan out from there (e.g., a fair sized subgraph under BUNDLE-OP). >> How is the overriding to be managed? >> > I suppose the trick is as follows: > 1- move the crucial behavior of downward-operation, sideway-operation, > selfward-operation, in separate defun's that are called by the > respective defmethods. > 2- have methods on operation that check whether the operation is > a subtype of any of the three above or non-propagating-operation. > If not — then apply the methods for all of them. > 3- at instantiation-time, call the same detection function, and issue a > WARNING. > In six months or a year, it will be replaced by a CERROR, then an ERROR, > at which point the defuns can be merged back into the respective defmethods. > > This way, people are warned now already, but ASDF keeps working, > and we don't break either all the software in quicklisp until later. > > Congratulations to Anton V. for this clever suggestion.
You have to be careful: If anybody defines :around methods, you will get surprising results. This is why the CLOS MOP forbids user code to define methods on pre-defined metaclasses, where a very similar trick is used to bottom out the reflective tower - specified generic functions on standard-xyz classes test whether the class of the metaobject parameter is exactly standard-xyz or a subclass, and branch accordingly. You may want to specify similar restrictions on user code to prevent such surprises. I also strongly advise against turning warnings into cerror or error. It just prevents working code from continuing to work, which is gratuitous IMHO. Pascal -- Pascal Costanza The views expressed in this email are my own, and not those of my employer.
