Le 11/05/13 11:54, Roland Bock a écrit :
On 2013-05-08 18:08, Vicente J. Botet Escriba wrote:
Hi,
as the conversion between concrete dates could be expensive I guess that these conversion must be explicit.
But this has some consequences when used the implicit conversion was hidden a not efficient implementation, e.g.
date ISO_week_start = mon <= jan/day(4)/y;
jan/day(4)/y should be ymd_date as is the efficient representation.
The date generator was declared as
date operator<=(weekday wd, date x); Hi,
Do you really want to allow/document/support/advocate the American date format in C++? Why not restrict the format to something close to ISO date format for ISO C++? That way you could introduce a new type, say ym_type and
ym_type operator/(year y, month m); date operator/(ym_type ym, day d);
Neither explicit nor implicit conversion necessary :-) We have suggested a more neutral factory
auto dt = make_date(year(2013), may, 11);
Another question I have about this is: Is is really a good idea to use operator/()? It does prevent you from calculating ratios between periods, e.g.
int ratio = year(3)/month(4); // ratio = 9
I'd therefore prefer another operator, e.g. operator <<
year,month and day are unit specifiers not periods (years, months, days). The ratio is obtained using int ratio = years(3)/months(4); // ratio = 9
But to be completely honest: I don't see the benefit of constructing dates this way. Why not simply use a constructor?
date(year, month, day);
With C++11 you could then write:
date ISO_week_start = mon <= { y, jan, day(4) }; I guess this depends on the type of {y, jan, day(4)} and the expected type of the rhs of the operator<= ? ??? operator <=(month, ???)
Note that we are talking of several dates types. { y, jan, day(4) } would be accepted where a ymd_date is expected. The operator <= is defined on serial_date as the algorithm is efficient only with this representation.
That's the way I'd prefer :-)
In order to support ymd_date ISO_week_start = mon <= { y, jan, day(4) }; we need to define operator <= for ymd_date or as a template, template <typename Date> Date operator <=(month,Date); but the implementation would do a conversion from Date to serial_date and return the conversion of the calculated serial_date to a Date. Best, Vicente