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Description:

time machine

The Dart Time Machine is a date and time library for
Flutter, Web, and Server
with support for timezones, calendars, cultures, formatting and parsing.
Time Machine provides an alternative date and time API over Dart Core.
For comparision:
Dart Core API

Duration - an amount of time with microsecond precision
DateTime - a unique point on the utc_timeline or a point in localtime with microsecond or millisecond precision

Time Machine API

Time - an amount of time with nanosecond precision
Instant - a unique point on the utc_timeline
LocalTime - the time on the clock
LocalDate - the date on the calendar
LocalDateTime - a location on the clock and calendar
Period - amount of time on the clock and calendar
Offset - the timezone offset from the utc_timeline
DateTimeZone - a mapping between the utc_timeline, and clock and calendar locations
ZonedDateTime - a unique point on the utc_timeline and a location on the clock and calendar
Culture - formatting and parsing rules specific to a locale

Time Machine's Goals

Flexibility - multiple representations of time to fit different use cases
Consistency - works the same across all platforms
Testable - easy to test your date and time dependent code
Clarity - clear, concise, and intuitive
Easy - the library should do the hard things for you

The last two/three? are generic library goals.
Time Machine is a port of Noda Time; use it for all your .NET needs.
Current TZDB Version: 2022a
Example Code: #
// Sets up timezone and culture information
await TimeMachine.initialize();
print('Hello, ${DateTimeZone.local} from the Dart Time Machine!\n');

var tzdb = await DateTimeZoneProviders.tzdb;
var paris = await tzdb["Europe/Paris"];

var now = Instant.now();

print('Basic');
print('UTC Time: $now');
print('Local Time: ${now.inLocalZone()}');
print('Paris Time: ${now.inZone(paris)}\n');

print('Formatted');
print('UTC Time: ${now.toString('dddd yyyy-MM-dd HH:mm')}');
print('Local Time: ${now.inLocalZone().toString('dddd yyyy-MM-dd HH:mm')}\n');

var french = await Cultures.getCulture('fr-FR');
print('Formatted and French ($french)');
print('UTC Time: ${now.toString('dddd yyyy-MM-dd HH:mm', french)}');
print('Local Time: ${now.inLocalZone().toString('dddd yyyy-MM-dd HH:mm', french)}\n');

print('Parse French Formatted ZonedDateTime');

// without the 'z' parsing will be forced to interpret the timezone as UTC
var localText = now
.inLocalZone()
.toString('dddd yyyy-MM-dd HH:mm z', french);

var localClone = ZonedDateTimePattern
.createWithCulture('dddd yyyy-MM-dd HH:mm z', french)
.parse(localText);

print(localClone.value);
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VM #

Flutter #

Web (Dart2JS and DDC) #

All unit tests pass on DartVM and DartWeb (just Chrome at this time).
Tests have been run on preview versions of Dart2,
but the focus is on DartStable, and they are not run before every pub publish.
The public API is stabilizing -- mostly focusing on taking C# idiomatic code
and making it Dart idiomatic code, so I wouldn't expect any over zealous changes.
This is a preview release -- but, I'd feel comfortable using it. (Author Stamp of Approval!)
Documentation was ported, but some things changed for Dart and the documentation is being slowly updated (and we need
an additional automated formatting pass).
Don't use any functions annotated with @internal. As of v0.3 you should not find any, but if you do, let me know.
Todo (before v1):

Port Noda Time
Unit tests passing in DartVM
Dartification of the API

First pass style updates
Second pass ergonomics updates
Synchronous TZDB timezone provider
Review all I/O and associated classes and their structure
Simplify the API and make the best use of named constructors

Non-Gregorian/Julian calendar systems
Text formatting and Parsing
Remove XML tags from documentation and format them for pub (human second pass still needed)
Implement Dart4Web features
Unit tests passing in DartWeb
Fix DartDoc Formatting
Create simple website with examples (at minimal a good set of examples under the examples directory)

External data: Timezones (TZDB via Noda Time) and Culture (ICU via BCL) are produced by a C# tool that is not
included in this repository. The goal is to port all this functionality to Dart, the initial tool was created for
bootstrapping -- and guaranteeing that our data is exactly the same thing that Noda Time would see (to ease porting).
Future Todo:

Produce our own TSDB files
Produce our own Culture files
Benchmarking & Optimizing Library for Dart

Flutter Specific Notes #
You'll need this entry in your pubspec.yaml.
# The following section is specific to Flutter.
flutter:
assets:
- packages/time_machine/data/cultures/cultures.bin
- packages/time_machine/data/tzdb/tzdb.bin
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Your initialization function will look like this:
import 'package:flutter/services.dart';

WidgetsFlutterBinding.ensureInitialized();

// TimeMachine discovers your TimeZone heuristically (it's actually pretty fast).
await TimeMachine.initialize({'rootBundle': rootBundle});
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Once flutter gets Isolate.resolvePackageUri functionality,
we'll be able to merge VM and the Flutter code paths and no asset entry and no special import will be required.
It would look just like the VM example.
Or with: https://pub.dartlang.org/packages/flutter_native_timezone
import 'package:flutter/services.dart';

// you can get Timezone information directly from the native interface with flutter_native_timezone
await TimeMachine.initialize({
'rootBundle': rootBundle,
'timeZone': await Timezone.getLocalTimezone(),
});
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DDC Specific Notes #
toString on many of the classes will not propagate patternText and culture parameters.
Instant and ZonedDateTime currently have toStringDDC functions available to remedy this.
This also works:
dynamic foo = new Foo();
var foo = new Foo() as dynamic;
(foo as dynamic).toString(patternText, culture);
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We learned in Issue:33876 that dynamic code uses a different flow path.
Wrapping your code as dynamic will allow toString() to work normally. It will unfortunately ruin your intellisense.
See Issue:33876 for more information. The fix
exists, now we just wait for it to hit a live build.
toStringDDC instead of toStringFormatted to attempt to get a negative
contagion coefficient. If you are writing on DartStable today
and you need some extra string support because of this bug, let me know.
Update: Dart 2.0 stable did not launch with the fix. Stable release windows are 6 weeks.
Hopefully we get the fix in the next release (second half of September).