[phobos] datetime review

[Walter Bright]

Jonathan M Davis wrote:
> On Friday, October 08, 2010 14:58:35 Walter Bright wrote:
>   
>>
>> It bothers me that there are so many types, i.e. "various duration
>> types", "various interval types", etc.
>>
>> Now that I read that again, why is there both a "duration" and an
>> "interval"?
>>     
>
> A duration is a length of time with units while an interval is two time points 
> (or a time point and a duration) which therefore designate a duration which is 
> fixed in time.

Ok, makes sense.

>  So, they are distinct (the concepts are from Boost). There are 
> multiple duration types primarily because you can't convert between months and 
> small units without a specific date, so you can't convert something like 5 months 
> to days without knowing which months you're dealing with.

True, but why would a month be a type other than int?

>  However, I have 
> definite worked on making it so that you don't have to worry about the multiple 
> duration types in most cases. You'd do something like Dur.years(5) + Dur.days(2) 
> to create a duration of 5 years and 2 days, and you don't have to know or care 
> what the duration types are.
>   

Ok, but I don't see that requires more than one duration type.

> There are multiple interval types only to deal with infinity. You have Interval, 
> with a definite begin and end, PosInfInterval which goes from a specific time 
> point to infinity, and NegInfInterval which goes from negative infinity to a 
> specific time point. The infinite intervals are primarily of interest in creating 
> infinite ranges. A lot of user code could simpler ignore them.
>   

Ok.

>   
>> Why are there multiple "various time zone classes" instead of "a" time
>> zone class?
>>     
>
> There are multiple time zone classes because it uses polymorphism to deal with 
> the rules for a given time zone. The really basic LocalTime and UTC deal with 
> most cases, but for anyone who really needs to deal with multiple time zones, 
> PosixTimeZone and WindowsTimeZone will be invaluable (I'd love to only have one 
> of those, but Windows just doesn't deal with time zones like the Posix world 
> does).
>
>   

I agree some kind of polymorphism for time zones is necessary. [rant] 
Timezones should be an operating system service, if for no other reason 
than it sucks to have all your apps break when some tinhorn country 
decides to change their daylight savings time, etc.[/rant]