sealed_language_extensions #

A pure Dart package that provides the IANA Language Tag Extensions Registry (BCP 47 / RFC 5646 §3.7) as compile-time constant, tree-shakable, sealed classes.

The data is regenerated automatically from the canonical IANA source.

Features #

• Every registered extension as a const instance (currently t and u).
• A sealed [LanguageTagExtension] hierarchy with one concrete subclass per extension, enabling exhaustive switch matching.
• Static entry points on LanguageTagExtension: list, map, fromIdentifier/maybeFromIdentifier (accepting any Object and an optional subset), maybeFromValue, a verbose toString({bool short}), and toMap/toJson/fromJson — mirroring the sealed_regions/sealed_languages API.
• Case-insensitive lookup by identifier.
• No third-party dependencies.

Usage #

import 'package:sealed_language_extensions/sealed_language_extensions.dart';

void main() {
  for (final extension in LanguageTagExtension.list) {
    print('${extension.identifier}: ${extension.description}');
  }

  // Case-insensitive lookup (nullable and throwing variants).
  final unicode = LanguageTagExtension.maybeFromIdentifier('U');
  print(unicode?.description); // Unicode Locale
  final transformed = LanguageTagExtension.fromIdentifier('t');

  // Exhaustive pattern matching over the sealed hierarchy.
  final label = switch (transformed) {
    SpecifyingTransformedContentExtension() => 'transform',
    UnicodeLocaleExtension() => 'locale',
  };
  print(label); // transform
}

Versioning #

This package uses a hybrid SemVer/CalVer scheme: 1.<yyyy><mm>.<d>, derived from the registry's File-Date (the date IANA published the data). For example, the extensions registry dated 2014-04-02 is published as 1.201404.2.

Data source & license #

The package code is © 2026 TigerC10, released under the MIT license (see LICENSE). The embedded data is sourced from the public IANA registry and remains subject to its terms.