On Mar 15, 2011, at 2:00 PM, Vicente Botet wrote:
Joachim Faulhaber wrote:
To summarize, for a domain type Dom, Icl expects Dom(), <, ++, -- and if dom is a equidistant scalar type we expect an associated type Dom::difference_type to be defined.
This choice has not been taken for chrono::durations, which is a little inconsistent also, because interestingly for its chrono::time_point type the semantic is just the desired one.
Yes, you are surely right. time_point could have a default constructor, and have a epoch function. Howard, what do you think?
The current std::chrono::duration default constructor has this definition: constexpr duration() = default; The rationale for this is to give the client and the Rep author as many options as possible: typedef std::chrono::duration<long long> D; D d1; // d1.count() uninitialized - speed D d2 = D(); // d2.count() zero-initialized - safety if you believe 0 is safe typedef std::chrono::duration<BigInt> CustomD; CustomD d3; // d3.count() default constructed The author of BigInt may decide that 0 is the best default value. *Or* he might decide that nan is the best default value (personally I'd be tempted to go with nan). We did not want to dictate that a default-constructed duration always represented zero, as this decision would have dubious qualities from a safety point of view. For time_point a default constructed object is specifically documented to have the value "epoch", and duration's static zero() function is used to initialize it. It was felt this was more useful for time_point. Though time_point will most often be constructed from the value returned by now(). -Howard