kosher_rust

Dart bindings for the kosher-rust crate. They cover the Jewish calendar, halachic times (zmanim) and daily learning schedules, and they work in plain Dart and in Flutter.

import 'package:kosher_rust/kosher_rust.dart';

Future<void> main() async {
  await initKosherRust();

  const date = (year: 2024, month: 4, day: 23);
  final today = HebrewDate.fromGregorian(date: date)!;
  print(today); // 15 Nisan 5784
  print(dafYomiBavli(date: today)); // Bava Metzia 55

  final jerusalem = Location(latitude: 31.778, longitude: 35.235);
  final zmanim = ZmanimCalculator(
    location: jerusalem,
    date: date,
    offset: TimeZone.local.offset,
  );
  print(await zmanim.time(zman: Zman.sunset)); // seconds since the Unix epoch

  disposeKosherRust();
}

Call initKosherRust once, and wait for it, before using anything else. A command-line program calls disposeKosherRust when it is done, because the open library keeps the program running. A Flutter app doesn't need to.

Dates, times and time zones

Dates are GregorianDate records, such as (year: 2024, month: 4, day: 23). Times come back as whole seconds since the Unix epoch, and instants passed in are given the same way. Weekdays are numbers, 1 for Monday through 7 for Sunday. Lengths of time are Dart Durations.

The calculations read the time zone through TimeZone, which you implement with whatever time zone library you use. TimeZone.local is the device's zone, TimeZone.utc is UTC, and FixedTimeZone never changes. Pass the zone's offset method when you build ZmanimCalculator or MyZmanimCalculator, or use their withoutZone constructors. Getting a time is asynchronous, because it reads the time zone by calling back into Dart. Everything else is synchronous.

How the API differs from Rust

Most types and methods have the same names as in kosher-rust. These differ.

Rust	Dart
Zmanim, MyZmanim	ZmanimCalculator, MyZmanimCalculator, with time in place of get
zmanim::Config	ZmanimConfig, starting from ZmanimConfig.defaults() and changed with copyWith
ZmanimError	ZmanimException, thrown by time
HebrewDate::new, HebrewYear::new	HebrewDate.of, HebrewYear.of, which return null where Rust returns None
HebrewDate::try_from(date)	HebrewDate.fromGregorian
HebrewYear::get	HebrewYear.value
name(), hebrew()	displayName, hebrewName
Zman::description	Zman.describe
DafYomiBavli.on(date) and the other schedules	dafYomiBavli(date: ...) and the other functions
Daf<BavliTractate>, Daf<YerushalmiTractate>	BavliDaf, YerushalmiDaf

Enums whose variants hold data, such as SpecialDay, AstronomicalCalculator and TehillimUnit, are sealed classes, so they compare with == and work in a switch. The portions of learning print as they do in Rust, for example "Nazir 5:5-6".

Location throws a LocationError for an invalid coordinate or elevation. A GregorianDate that does not exist, such as 30 February, throws an exception.

Running

Building needs rustup. The toolchain and its targets are in rust/rust-toolchain.toml. The first build compiles the Rust crate in release mode and takes a few minutes. Later builds reuse it.

dart test

dart run example/kosher_rust_example.dart

The example prints today's Hebrew date, learning and zmanim for Jerusalem, or for the latitude and longitude you pass, in this computer's time zone.

Project structure

• rust is the Rust crate the bindings are generated from. It depends on kosher-rust in the repository root, with the __dart_enabled feature, which makes SpecialDay and AstronomicalCalculator exhaustive so they can cross to Dart as sealed classes.
• hook is flutter_rust_bridge's build hook. It compiles the crate and bundles it with the package.
• lib has the Dart API and the generated bridge code. lib/src/loader.dart finds the bundled library, which flutter_rust_bridge's own loader does not do outside Flutter.
• example is the command-line program above.
• test has the tests.

Changing the bindings

flutter_rust_bridge scans kosher-rust itself, so its enums and plain structs, with their documentation, cross to Dart as they are. Two folders in rust/src adjust that.

• third_party/kosher_rust holds attributes for kosher-rust's own items, such as one to leave a method out or to make a type opaque. Each module mirrors the kosher-rust module the items are in.
• api has what Dart can't call as it is. That covers methods that take self, names returned as &'static str, the calculators that are generic over their time zone, the config and error types, and the conversions for jiff's types.

After changing either, or kosher-rust's public API, regenerate the Dart code from this directory.

flutter_rust_bridge_codegen generate

The code generator's version must match the flutter_rust_bridge versions in pubspec.yaml and rust/Cargo.toml, which is 2.13.0.