Subject: Re: [boost] [chrono/date] Unit specifiers arithmetic
From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2013-05-06 10:10:16
On May 6, 2013, at 9:55 AM, "Vicente J. Botet Escriba" <vicente.botet_at_[hidden]> wrote:
> Le 06/05/13 15:34, Howard Hinnant a écrit :
>> On May 6, 2013, at 6:31 AM, "Vicente J. Botet Escriba" <vicente.botet_at_[hidden]> wrote:
>>> Moving from checked dates to unchecked ones by default and forcing to user the Unit specifiers year/month/day in any date constructor (even the unchecked ones) has some ugly consequences. Note that I was able to build an unchecked date as
>>> date d(2013,5,6, no_check);
>>> year y;
>>> month m;
>>> day d;
>>> the following will not compile now as the constructors expects a year but y+1 is an int.
>>> date d(y+1, m, d);
>>> The user needs to type
>>> date d(year(y+1), m, d);
>>> Is this what we want to provide to the user or should we add basic arithmetic on these unit specifiers?
>> This is an example of where flexible ordering and implicit last unit starts to shine. Examples from my 2011 paper:
>> start = mon <= jan4/(d.year()-1);
>> date next_start = mon <= jan4/(start.year()+1);
>> Or translated to your example and syntax:
>> date d(d, m, y+1); // works because last unit can be int
> Last unit or any unit but only one?
Any two explicit units should disambiguate. We could even take it more lax than that and still avoid ambiguity if desired.
A warning though: We want to make the checked syntax more attractive than the unchecked syntax, else all dates will be unnecessarily unchecked in practice.
>> If we start adding arithmetic to the unit specifier day, it becomes indistinguishable from a duration. Now it is possible that we could use durations as unit specifiers.
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk