Steven Schveighoffer wrote:
On Sun, 26 Apr 2009 21:20:32 -0400, Andrei Alexandrescu
I think, all other things being equal, that opApply tends to be slower
than iterators.
It depends. The range must have either inline-able functions, or must
NOT call virtual functions. Otherwise, it could be worse. there is
also the factor that you are using an inner function with opApply, so if
you regularly access variables outside the foreach loop, then those add up.
Observe that in opapply style, you do one delegate call per loop iteration.
With range style, you do three calls on the range per loop iteration
(empty, front, popFront).
If those range calls call virtual calls or ARE virtual calls, then range
loses. Of course, the difference might be washed if you do lots of
accesses to an outer variable in your foreach loop, which require a
pointer dereference vs. a stack dereference.
We should quantify this and see what the actual performance is.
This is a very good point. If a range offers virtual
empty/popFront/front, then opApply is a faster proposition. This makes
for a good use case for making opApply the preferred way of iteration,
if present (if you just do foreach and opApply is present, use it).
Andrei
