AMDG On 05/28/2011 11:08 AM, Vicente Botet wrote:
Steven Watanabe-4 wrote:
On 05/28/2011 09:42 AM, Vicente Botet wrote:
In the definition of the concept less_than_comparable in Boost.Any, you define the implementation of these operators in function of operator<(), but if the types provide the specific signature the specific function is not called. I guess that the default implementation of for example operator<= should use operator< only if the the underlying types don't provide operator<=.
I don't think this is worth the extra complexity. Do you know of any real case where it will either a) change the behavior of a program or, b) make the program more efficient?
It will definitely make the vtable larger.
I don't know if these are real cases, but we could imagine a class that is counting the number of calls to each operator, or making some performance measures by operator, some specific logging, ...
This is definitely going to be rare, but regardless, no algorithm using these operators is going to guarantee that it uses > instead of <. It's going to assume that it can use them interchangeably and use whichever is most convenient.
I agree that your design works most of the time, and that taking care of these specific cases needs to define several apply function in the concept (vtable), but I think that it will be really surprising for a user expecting that his specific implementation is not called.
I still don't think a specific implementation makes much sense for LessThanComparable. Currently all algorithms that require an ordering use operator< only and I haven't heard any complaints. I see the ability to use the other operators as a convenience more than anything else.
I don't think this will make the program more efficient, but more consistent.
I don't have the concepts proposal handy, but doesn't LessThanComparable have an axiom that requires that (a < b) is equivalent to (b > a)?
It would be unhappy if a user will not use the concepts provided by the library just due to this restriction.
I don't see this happening in this case. Ever.
Anyway, if you decide to maintain your design, it will be worth documenting the behavio with the current restriction.
I think it is documented. In Christ, Steven Watanabe