Probably because he (as a clojure developer) likes immutability of data structures. On Tue, Nov 29, 2011 at 9:15 PM, Maciej Fijalkowski <fijall@gmail.com>wrote:
On Tue, Nov 29, 2011 at 10:12 PM, Alex Gaynor <alex.gaynor@gmail.com> wrote:
On Tue, Nov 29, 2011 at 3:04 PM, Timothy Baldridge <tbaldridge@gmail.com
wrote:
I have a dictionary (in RPython) that looks something like this:
class MyDict(Obj): def add(self, k, v): newdict = self.dict.copy() newdict[k] = v self.dict = newdict def get(self, k): d = self.dict return MyDict._static_get(d, k) @staticmethod @purefunction def _static_get(d, k): if d not in k: return None return d[k]
I'm trying to figure out the best way to optimize this. As you see, this structure is "append only". That is if mydict.get("foo") returns a value it will always return that value, for all time. In that sense, the function is pure. If however, the function returns None, then it could change in the future.
This is for my Clojure on PyPy implementation. The idea is that types can be extended via protocols, at runtime, at any point in the program's execution. However, once a given type is extended to support a given interface (or protocol) it will never be able to be changed. That is, once we extend Foo so that it implements Foo.count() it will implement Foo.count() for all time.
Any thoughts on how to optimize this further for the jit? I'd like to promote the value of get() to a constant, but I can only do that as long as it is not None. After Foo is extended, I'd like the jit to re-generate the jitted code to remove all guards, hopefully saving a few cycles.
Timothy
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Sounds like the idea you're looking for is basically out-of-line guards. Basically the idea of these is you have field which rarely changes, and when it does you should regenerate all code. So you would have an object with the dict and a signature, and you could mutate the dict, but
whenever
you did, you'd need to update the signature. PyPy's module-dictionary implementation shows an example of this: https://bitbucket.org/pypy/pypy/src/default/pypy/objspace/std/celldict.py
Alex
-- "I disapprove of what you say, but I will defend to the death your right to say it." -- Evelyn Beatrice Hall (summarizing Voltaire) "The people's good is the highest law." -- Cicero
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Why do you always make a copy of a dict btw? _______________________________________________ pypy-dev mailing list pypy-dev@python.org http://mail.python.org/mailman/listinfo/pypy-dev