On 27/04/12 18:02, Steven Schveighoffer wrote:
Hm.. you have marked all your functions pure as well. I don't think this will
affect anything in the current implementation, but it might. However, I'd expect
the opposite (const version is faster) if anything.
Yes, me too, hence confusion.
I have to say I'm somewhat confused about whether the pure markings are really
accurate. The reputation() modifies the reputationUser_ and reputationObject_
internal arrays and hence the returned values of reputationUser() and
reputationObject(). It's true that for a given input to reputation(), the
outcome will always be the same, but there's nevertheless mutability involved:
if I pass one input to reputation(), and then another, the reputationObject()
and ...User() outputs will change as a result.
I suppose it's a kind of weak purity, but I'm not too happy with it. I suppose
I could get reputation() to _return_ reputationObject and reputationUser instead
of having them called via functions; but I'd be worried it would slow everything
down substantially.
Background to this piece of code: it's a D rewrite of some C++ I wrote a couple
of years back as part of a research project. I took quite a lot of time to make
the C++ as efficient as possible, so this is a nice test case to see if I can
get D to produce similar efficiency while having much more elegantly-written
code. It's also just a nice way to learn to be "D-ish", working on a problem
that I already understand well.
Currently the D code is MUCH more elegant and easy to read than the C++, and
runs about 2 seconds slower for the test case implemented here (so on my
machine, C++ does it in about 21s as opposed to D's 23), with that difference
scaling with problem size. It's a tolerable difference, though it would be nice
to see if I can close the gap.
