Carl Banks wrote: > On Jan 23, 8:22 pm, Bryan Olson <fakeaddr...@nowhere.org> wrote: >> Paul Rubin wrote: >>> Bryan Olson writes: >>>>> BTW, class instances are usually immutable and thus don't require a >>>>> mutex in the system I described. >>>> Then you are describing a language radically different from Python. >>> That one threw me for a minute too, but I think the idea is that the >>> class instance itself is immutable, while its slots (specifically the >>> attribute dictionary) point to mutable objects. >> The meaning of 'immutable' is well-established in the Python literature. >> Python's immutable types include tuple, frozenset, and various kinds of >> numbers and strings. Class instances, not so much. > > Of course class instances aren't immutable types: they're not even > types. Let me suggest that there is a distinction between an > immutable type and an immutable object. > > Immutable types are what you are talking about: it means that the type > provides usable mutator methods. (Whether they mutate the object > itself or some associated object doesn't matter.) Immutable objects > are a different thing: it means the object cannot change in memory. > > Classes in Python are mutable types, usually. Class instances are > (except for the refcount) immutable objects, usually. > > We usually talk about mutability of types, but mutability of objects > is appropriate for discussion as well. So I can't really agree with > your assessment that I wrong to call class instances immutable objects > aside from refcounts. > > BTW, here's a minor brain bender: immutable types are mutable objects. > > >> What's more, this matters when considering a GIL-less implementation. >> Typical method calls can traverse lots of mutable stuff just to find the >> function to invoke. > > Now that doesn't make sense at all. What is all this mutable stuff > you have to go through, and what does it have to do with the GIL-less > implementation? Can you explain further? Or are you just saying > it'll be slow. > OK, so we have recently discussed whether objects are values, whether function arguments are passed by reference, whether names are references, and now we are, I suspect, about to have a huge further discussion on the meaning of "immutable".
Sometimes I start to find this eternal pedantry a little tedious. I suspect it's time I once more dropped out of c.l.py for a while. regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
