On 14/12/2016 18:47, Markus Armbruster wrote: > Paolo Bonzini <pbonz...@redhat.com> writes: > >> On 14/12/2016 14:48, Eduardo Habkost wrote: >>>> How do you find all abstract TypeInfo in the source? The uninitiated >>>> might grep for .abstract = true, and be misled. The initiated will be >>>> annoyed instead, because grepping for *absence* of .instance_size = is >>>> bothersome. >>>> >>>> I suspect life could be easier going forward if we instead required >>>> .abstract = true for interfaces, and enforced it with >>>> assert(ti->instance_size || ti->abstract) here. >>> I was doing that before deciding to change type_initialize(). I >>> think I still have the commit in my git reflog, I will recover it >>> and submit it as v3. >> >> I think it's worse. >> >> Interfaces are abstract by definition. Requiring ".abstract = true" >> makes things less intuitive. v2 seems good. > > What makes a TypeInfo declaration an interface? Whatever it is, it > better be *locally* obvious.
The fact that the superclass is an interface: 1) most interface names are (or should be) "interfacey". Compare device, memory backend, console (all classes) with user-creatable, fw path provider, hotplug handler. A few others simply end with "_IF". Of course naming is the hardest problem in computer science so there are some interfaces whose name might apply just as well to a class (stream slave, ISA DMA). However... 2) ... currently we don't have a single case of an interface that doesn't inherit from TYPE_INTERFACE, so all interfaces are declared with ".parent = TYPE_INTERFACE". That does make a TypeInfo obviously an interface. If we ever have a case of interface inheritance, the supertype had better have a good name. Paolo
