On 7 Mar 2011, at 06:34, Joel Falcou wrote:
On 07/03/11 03:25, Peter Dimov wrote:
I probably should note that expression templates require CoW, as far as I can see; if you return an expression from a*b instead of computing the product, the expression needs to keep a and b alive. Having it store copies would defeat the purpose. Storing references wouldn't work well in generic code such as a forwarding function. Even something as simple as auto x = f() + y; would be a subtle bug. Well , ET based code usually keep references to large terminals. the 'auto'/ET interaction is known and is likely to never occurs. And if needed, well, that's what proto::deep_copy is for.
So users of a expression-template based xint would need to know about proto::deep_copy? Also, I would expect these problems to become more serious in C++0x code, because users will probably write expressions like: auto i = x + y; Which would be fine for built-in types, and introduce bugs if x or y was an xint::integer, using proto. Chris