On Aug 25, 2007, at 3:10 PM, Peter Dimov wrote:
Howard Hinnant:
I'm strictly looking at this from the client's point of view. I'm the client. I know what I want, and I want to be able to pick something and know what it does. I don't want to be stuck with something that maybe does something, and maybe not. It's like buying something with absolutely no warranty.
No, I don't agree. This is like saying that if the car you bought promises 40 MPG and delivers 45, you'd return it because it doesn't meet the spec.
Bad analogies aside, giving the implementation the opportunity to check the assumptions of your code is not as worthless as you make it to be. It does not just "add a bunch of undefined behavior", it adds a license for the implementation to turn the already erratic behavior into a predictable assertion failure.
If the client has used the mutex constructor, this means that his code has already made the assumption that the condition will be used with that mutex. If you take away the Requires clause (the "bunch of undefined behavior"), this will not make the code any more correct and can never be an improvement; it would be, at worst, a tie if the implementation did no checking.
The main philosophical difference between us is that I want to be able to choose "check", and be assured that I'm actually getting checking. And then I want to be able to choose "don't check". And then not have to pay for it. I want both choices. What I want: std::condition<std::constrain<std::mutex>> cv(mut); // I *know* that if I mix bindings, I will get some kind of noise And then I want to be able to change that code: // I *know* that I'm not paying for checking std::condition<std::mutex> cv(mut); // Either with or without the "mut", I don't care With your proposal I write: std::condition<std::mutex>> cv(mut); and I don't know whether I have checking or not. All I know is that I've given permission for the implementation to check. And if I write: std::condition<std::mutex>> cv; Then I don't know that I'm not still paying for checking. I want your (1) and (3). Your (2) gives me neither, not both. -Howard