On 05/31/2011 01:07 PM, Vitja Makarov wrote:
2011/5/24 Stefan Behnel<stefan...@behnel.de>:
Vitja Makarov, 23.05.2011 21:33:
2011/5/23 Stefan Behnel:
However, once we really know which values change between yield calls,
i.e.
which ones need to be stored away, it will actually be less expensive in
most cases. We currently pay the indirection penalty for each access,
even
read access, whereas the C compiler can then keep important variables in
registers and only write them back once per yield.
I think that all not NULL variables should be saved/restored inside yield.
I can not really track changes only assignments.
I mean "assignments" when I write "changes". When a variable is being
assigned to, we should assume that its value changed. Users can be expected
to be smart enough to avoid unnecessary assignments in most cases, there's
no need to put work into optimising them away automatically.
for i in a:
yield i # j is NULL here
for j in b:
yield j # a, b, i ,j should be saved/restored
Right. However, in general, we can expect that most variables will have been
initialised on a yield.
We can still avoid storing away C typed variables that are not being used
later on, because they are not reference counted.
And if the user sets 'a' and 'i' to None between the loops, they won't need
to be saved on the second yield either. But that's an optimisation, not a
requirement.
What about copying C++ structs and objects with constructor (and/or
overloaded = method)?
That wouldn't work well.
Currently I believe C++ objects are only supported through pointers,
which of course are copyable. If or when we support C++ objects on the
stack, then we should definitely avoid copying them.
If you declare a C++ class as a struct Cython-side then I think we
should assume that we can freely invoke the copy constructor and
assignment operator in this context.
Dag Sverre
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