Ticket #778 (closed RFC: duplicate)
Make FileHandle Subclassable
|Reported by:||whiteknight||Owned by:|
|Severity:||medium||Keywords:||io oo pmc|
There were some other related tickets (I can't find them now) about this, so sorry if I am duplicating anything.
FileHandles are not current subclassable in PIR because they have ATTRs that are not usable from PIR (char*, PIOOFF_T, etc). In order for a PMC like FileHandle to be properly subclassable, every one of it's ATTRs must be an INTVAL, FLOATVAL, STRING* or PMC*. Otherwise, the subclass will throw an exception if we try to access an ATTR that is not one of these from the parent type.
I want to make two changes to FileHandle (in addition to the cleanups I am working on in the io_cleanups branch right now) to make this possible:
1) Create a new IOBuffer PMC type to take care of buffering. FileHandle will then delegate it's buffering needs to a PMC of this type. The benefit here is that we can use this same buffering functionality from other IO PMC types (sockets, pipes, etc). 2) Convert the ATTRs file_pos and last_pos from type PIOOFF_T into type INTVAL. This may be a lossy transition but it's worth noting that almost every use of these two ATTRs, outside the IO API, are converted to INTVAL already.
#2 of course is a little sketchy, so I would be happy to hear about alternate ideas to fix this issue. Shortly after getting these ATTRs fixed (if not immediately thereafter) we should be able to properly subclass FileHandles.