Create a NodaTime LocalDate representing "today"

Question

What is the recommended way to create a LocalDate instance that represents "today". I was expecting there to be a static "Now" or "Today" property in the LocalDate class, but there isn't. My current approach is to use DateTime.Now:

var now = DateTime.Now;
LocalDate today = new LocalDate(now.Year, now.Month, now.Day);

Is there a better way?

Matt Johnson-Pint · Accepted Answer · 2015-01-09T04:44:19.123

First recognize that when you say "today", the answer could be different for different people in different parts of the world. Therefore, in order to get the current local date, you must have a time zone in mind.

Noda Time correctly models this by giving you an Instant when you call Now from an IClock implementation such as the system clock. An instant is universal, so you just need to convert it to some time zone to get that time zone's local date.

// get the current time from the system clock
Instant now = SystemClock.Instance.Now;

// get a time zone
DateTimeZone tz = DateTimeZoneProviders.Tzdb["Asia/Tokyo"];

// use now and tz to get "today"
LocalDate today = now.InZone(tz).Date;

That's the minimal code. Of course, if you want to use the computer's local time zone (like you did with DateTime.Now), you can get it like so:

DateTimeZone tz = DateTimeZoneProviders.Tzdb.GetSystemDefault();

And to really implement it properly, you should call .Now from the IClock interface, such that you could substitute the system clock with a fake clock for your unit tests.

This is a great example of how Noda Time intentionally doesn't hide things from you. All this is still going on under the hood when you call DateTime.Now, but you just don't see it. You can read more about Noda Time's design philosophy in the user guide.

score 19 · Answer 2 · answered Jan 10 '15 at 12:43

19

Matt's answer is spot on for Noda Time 1.x.

In Noda Time 2.0, I'm introducing a ZonedClock, which is basically a combination of IClock and a DateTimeZone. As you're likely to want the current time in the same time zone multiple times, you can inject that (I'm assuming you're using dependency injection) and retain that, then use it. For example:

class SomeClass
{
    private readonly ZonedClock clock;

    internal SomeClass(ZonedClock clock)
    { 
        this.clock = clock;
    }

    internal void DoSomethingWithDate()
    {
        LocalDate today = clock.GetCurrentDate();
        ...
    }
}

You would normally provide the ZonedClock by taking an IClock and using one of the new extension methods, e.g.

var clock = SystemClock.Instance;
var zoned = clock.InUtc();
// Or...
var zoned = clock.InZone(DateTimeZoneProviders.Tzdb["Europe/London"];
// Or...
var zoned = clock.InTzdbSystemDefaultZone();
// Or...
var zoned = clock.InBclSystemDefaultZone();

Note that your 1.x code won't work in 2.x anyway - I'm removing the Now property from IClock as it really shouldn't be a property (given the way it changes) - it's now a GetCurrentInstant() method.;

answered Jan 10 '15 at 12:43

Jon Skeet

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I like it. 2.0 is looking better all the time! – Matt Johnson-Pint Jan 10 '15 at 19:16
What lifetime should `ZonedClock` be registered as when using DI? – Oskar Oct 23 '18 at 07:44
1

@Oskar: I don't really know how to answer that. Do you always want the same clock? Do you always want the same time zone? Use the answers to those questions to drive your choice. – Jon Skeet Oct 23 '18 at 09:18
I always want the same time zone. Is there any downside with using the same clock? – Oskar Oct 23 '18 at 09:28
1

@Oskar: Almost certainly not - but you're the one with all the context here. There's nothing special going on from the Noda Time side. – Jon Skeet Oct 23 '18 at 22:10

score 8 · Answer 3 · answered May 25 '18 at 14:15

8

Jon's answer is right, but I think it is helpful to put it all together. For NodaTime 2.x:

SystemClock.Instance.InTzdbSystemDefaultZone().GetCurrentLocalDateTime().Date

answered May 25 '18 at 14:15

Patrick Szalapski

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Create a NodaTime LocalDate representing "today"

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