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From: Phil Richards (news_at_[hidden])
Date: 2003-12-12 08:21:54

On 2003-12-12, David Abrahams <dave_at_[hidden]> wrote:
[in reply to me saying:]
> > The one worry I still have with the MPL approach when combined
> > with the dimension-tagging approach you've taken is the compile-time
> > performance - in its current form it is, frankly, unusable.
> Did you try using mpl::vector instead of mpl::list?

The problem isn't with mpl::list vs mpl::vector, I think.
The problem is using a sequence type to do set operations -
which is basically what Matthias does with his tagged
rationals. I suspect most of his algorithms drop into
O(n^2) (or worse) at compile time.

The MPL list/vector is (probably) going to be fine for the fixed
size dimensional analysis version but there is a bit of a
learning curve involved... and I would have most likely used it
if I could have got it to work. I just didn't have the patience,
I'm afraid. (And I suspect it would be not much difference
in compile-time performance to my current implementation.)

[My current implementation for dimensional analysis (still not on
yahoo groups) could quite easily have its dimensionality holding
class replaced.]


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