On 6/14/2010 2:10 AM, joel falcou wrote:
Eric Niebler wrote:
Heck, it's simple enough. I just checked in the fix on trunk. Let me know how that works for you.
OK the base case is working now. I just got a last small problem.
If I try to evaluate :
m = l+k, x = x + y;
with the former code given earlier and the latest trunk, the display of the evaluation is:
<snip>
Which means that the x = x+y expression is copied and destroyed four time despite my "no-eval" policy in the constructor of expr. I assume some temporary copy are made which are not captured by my no-eval code in nt2::containers::expr.
Did I missed some customization to make subdomain/domain expression be captured by reference or should I had some new copy constructor/operator= in my expression class in which I have to toggle the "no-eval" switch ?
I was mistaken about falling foul of RVO. Here is what is happening. You have two domains in play, both with different generators. You compose some expressions in different domains, A and B. Proto decides the resulting expression R should be in domain B. Proto prefers things to be nice and uniform, so before making A a child of R, it puts it also into B's domain by applying B's generator. That causes the extra copy you're seeing. If A and B had had the same generator, no extra invocation of the generator would be performed. Why does Proto put expression A into B's domain? Good question. It just seemed like the right thing to do when I wrote the code. Right now, that looks like a dubious decision. Lemme think on it for a bit. -- Eric Niebler BoostPro Computing http://www.boostpro.com