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digitalmars.D.learn - Adding days to std.datetime.Date

reply Piotr Szturmaj <bncrbme jadamspam.pl> writes:
Is it possible to add a particular number of days to a Date?

I have number of days since 1 Jan 2000 and I want to convert it to Date:

int days = read!int; // number of days since 1 Jan 2000
Date x = Date(2000, 1, 1);
x.add!"days"(days);

Unfortunately add() does not support adding days. Will it be possible in 
the future or is there another approach?

Thanks
Apr 07 2011
next sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 07 Apr 2011 15:07:02 -0400, Piotr Szturmaj <bncrbme jadamspam.pl>  
wrote:


 Is it possible to add a particular number of days to a Date?

 I have number of days since 1 Jan 2000 and I want to convert it to Date:

 int days = read!int; // number of days since 1 Jan 2000
 Date x = Date(2000, 1, 1);
 x.add!"days"(days);

 Unfortunately add() does not support adding days. Will it be possible in  
 the future or is there another approach?


Yes, use core.time.Duration.

Duration was moved to core so it could be used in core functions, like  
Thread.sleep.

so

x += dur!"days"(days);

See: http://www.digitalmars.com/d/2.0/phobos/core_time.html#dur

-Steve
Apr 07 2011
parent Piotr Szturmaj <bncrbme jadamspam.pl> writes:
Steven Schveighoffer wrote:

 On Thu, 07 Apr 2011 15:07:02 -0400, Piotr Szturmaj
 <bncrbme jadamspam.pl> wrote:


 Is it possible to add a particular number of days to a Date?

 I have number of days since 1 Jan 2000 and I want to convert it to Date:

 int days = read!int; // number of days since 1 Jan 2000
 Date x = Date(2000, 1, 1);
 x.add!"days"(days);

 Unfortunately add() does not support adding days. Will it be possible
 in the future or is there another approach?


 Yes, use core.time.Duration.

 Duration was moved to core so it could be used in core functions, like
 Thread.sleep.

 so

 x += dur!"days"(days);

 See: http://www.digitalmars.com/d/2.0/phobos/core_time.html#dur


Well, I did find it few mins ago. But std.datetime's doc still states 
that it provide types to represent durations of time.


 -Steve


Thanks!
Apr 07 2011
prev sibling parent reply =?UTF-8?B?IlRow6lv?= Bueno" <munrek gmx.com> writes:
On Thursday, 7 April 2011 at 19:10:40 UTC, Piotr Szturmaj wrote:

 Is it possible to add a particular number of days to a Date?

 I have number of days since 1 Jan 2000 and I want to convert it 
 to Date:

 int days = read!int; // number of days since 1 Jan 2000
 Date x = Date(2000, 1, 1);
 x.add!"days"(days);

 Unfortunately add() does not support adding days. Will it be 
 possible in the future or is there another approach?

 Thanks


Is there any particular reason why std.datetime's "add" does not 
support days ?
Dec 02 2014
parent reply "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
On Tue, Dec 02, 2014 at 05:21:27PM +0000, via Digitalmars-d-learn wrote:

 On Thursday, 7 April 2011 at 19:10:40 UTC, Piotr Szturmaj wrote:

Is it possible to add a particular number of days to a Date?

I have number of days since 1 Jan 2000 and I want to convert it to
Date:

int days = read!int; // number of days since 1 Jan 2000
Date x = Date(2000, 1, 1);
x.add!"days"(days);

Unfortunately add() does not support adding days. Will it be possible
in the future or is there another approach?

Thanks


 
 Is there any particular reason why std.datetime's "add" does not
 support days ?


Sure it does:

	import std.datetime;
	import std.stdio;

	void main() {
		auto date = Date(2000, 1, 1);
		date += 10.days;
		writeln(date);
	}

Output:

	2000-Jan-11


T

-- 
Heads I win, tails you lose.
Dec 02 2014
parent reply =?UTF-8?B?IlRow6lv?= Bueno" <munrek gmx.com> writes:
On Tuesday, 2 December 2014 at 18:00:14 UTC, H. S. Teoh via 
Digitalmars-d-learn wrote:

 On Tue, Dec 02, 2014 at 05:21:27PM +0000, via 
 Digitalmars-d-learn wrote:

 On Thursday, 7 April 2011 at 19:10:40 UTC, Piotr Szturmaj 
 wrote:

Is it possible to add a particular number of days to a Date?

I have number of days since 1 Jan 2000 and I want to convert 
it to
Date:

int days = read!int; // number of days since 1 Jan 2000
Date x = Date(2000, 1, 1);
x.add!"days"(days);

Unfortunately add() does not support adding days. Will it be 
possible
in the future or is there another approach?

Thanks


 
 Is there any particular reason why std.datetime's "add" does 
 not
 support days ?


 Sure it does:

 	import std.datetime;
 	import std.stdio;

 	void main() {
 		auto date = Date(2000, 1, 1);
 		date += 10.days;
 		writeln(date);
 	}

 Output:

 	2000-Jan-11


 T


Indeed, thank you :)

But still, why this method 

"month" or "years" while this one
Dec 02 2014
parent reply =?UTF-8?B?IlRow6lv?= Bueno" <munrek gmx.com> writes:
 But still, why this method 

 supports "month" or "years" while this one 



But still, why this method 

"month" or "years" while this one 

days ?*
Dec 02 2014
parent reply "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
On Tue, Dec 02, 2014 at 06:49:54PM +0000, via Digitalmars-d-learn wrote:

But still, why this method

or "years" while this one



 
 But still, why this method

 "month" or "years" while this one

 ?*


Hmm. Looks like an oversight. File a bug?


T

-- 
"Computer Science is no more about computers than astronomy is about
telescopes." -- E.W. Dijkstra
Dec 02 2014
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 12/2/14 2:00 PM, H. S. Teoh via Digitalmars-d-learn wrote:

 On Tue, Dec 02, 2014 at 06:49:54PM +0000, via Digitalmars-d-learn wrote:

 But still, why this method

 or "years" while this one



 But still, why this method

 "month" or "years" while this one

 ?*


 Hmm. Looks like an oversight. File a bug?


Not an oversight.

Date.add and Date.roll are for adding units that are variable.

For example, how many days are in a month? Answer: depends on the month. 
How many days in a year? Answer: depends on the year.

But days are NOT variable, there are exactly 24 hours in a day. So to 
add a day, you just add a day with +=.

-Steve
Dec 02 2014
next sibling parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 12/2/14 2:14 PM, Steven Schveighoffer wrote:


 Not an oversight.

 Date.add and Date.roll are for adding units that are variable.

 For example, how many days are in a month? Answer: depends on the month.
 How many days in a year? Answer: depends on the year.

 But days are NOT variable, there are exactly 24 hours in a day. So to
 add a day, you just add a day with +=.


Aaaand to expand on this, since roll *does* support days, it's because 
the number being added isn't the important unit, it's the unit above. 
Hence rolling days means you will stay in the same month.

I'm not exactly sure of the reason behind roll, but I'm sure Jonathan 
has one :)

-Steve
Dec 02 2014
next sibling parent =?UTF-8?B?IlRow6lv?= Bueno" <munrek gmx.com> writes:
On Tuesday, 2 December 2014 at 19:21:35 UTC, Steven Schveighoffer 
wrote:

 On 12/2/14 2:14 PM, Steven Schveighoffer wrote:


 Not an oversight.

 Date.add and Date.roll are for adding units that are variable.

 For example, how many days are in a month? Answer: depends on 
 the month.
 How many days in a year? Answer: depends on the year.

 But days are NOT variable, there are exactly 24 hours in a 
 day. So to
 add a day, you just add a day with +=.


 Aaaand to expand on this, since roll *does* support days, it's 
 because the number being added isn't the important unit, it's 
 the unit above. Hence rolling days means you will stay in the 
 same month.

 I'm not exactly sure of the reason behind roll, but I'm sure 
 Jonathan has one :)

 -Steve


Oh well, this explanation make so much sense !

Unfortunately, I was not able to find it on the documentation :/

Thank you.
Dec 02 2014
prev sibling parent Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, December 02, 2014 14:21:35 Steven Schveighoffer via
Digitalmars-d-learn wrote:

 On 12/2/14 2:14 PM, Steven Schveighoffer wrote:


 Not an oversight.

 Date.add and Date.roll are for adding units that are variable.

 For example, how many days are in a month? Answer: depends on the month.
 How many days in a year? Answer: depends on the year.

 But days are NOT variable, there are exactly 24 hours in a day. So to
 add a day, you just add a day with +=.


 Aaaand to expand on this, since roll *does* support days, it's because
 the number being added isn't the important unit, it's the unit above.
 Hence rolling days means you will stay in the same month.

 I'm not exactly sure of the reason behind roll, but I'm sure Jonathan
 has one :)


A prime example of where to use it would be if you have a GUI with spinners
for the values, and you didn't want incrementing the day to increment the
month. It would be kind of annoying to implement that without roll. And
since you need to specify the units for rolling (and the addition operator
was already used for normal adding), adding a Duration to the time point in
order to roll didn't make sense, and a separate function was needed for it
even for the smaller units. I don't remember if roll originated with Boost,
or if I came up with it though (since portions of std.datetime's API are
based on Boost - e.g. julianDay is only there because Boost had it, and
astronomers use it such that it seemed useful enough to have; I wouldn't
have come up with it on my own though).

- Jonathan M Davis
Dec 06 2014
prev sibling parent Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, December 02, 2014 14:14:58 Steven Schveighoffer via
Digitalmars-d-learn wrote:

 On 12/2/14 2:00 PM, H. S. Teoh via Digitalmars-d-learn wrote:

 On Tue, Dec 02, 2014 at 06:49:54PM +0000, via Digitalmars-d-learn wrote:

 But still, why this method

 or "years" while this one



 But still, why this method

 "month" or "years" while this one

 ?*


 Hmm. Looks like an oversight. File a bug?


 Not an oversight.

 Date.add and Date.roll are for adding units that are variable.

 For example, how many days are in a month? Answer: depends on the month.
 How many days in a year? Answer: depends on the year.

 But days are NOT variable, there are exactly 24 hours in a day. So to
 add a day, you just add a day with +=.


Exactly. add wouldn't even exist if it weren't for the fact that Duration
doesn't work with units greater than weeks because of they depend on what
date you're talking about.

- Jonathan M Davis
Dec 06 2014