dtd

• Breaking Change: rename EventParameters constants to DtdParameters.
• Breaking Change: delete the kFileSystemServiceName constant in favor of FileSystemServiceConstants.serviceName.
• Breaking Change: delete the kUnifiedAnalyticsServiceName constant in favor of UnifiedAnalyticsServiceConstants.serviceName.
• Added CoreDtdServiceConstants and FileSystemServiceConstants for shared use among DTD clients.

Language

Dart 3.0 adds the following features. To use them, set your package's SDK constraint lower bound to 3.0 or greater (sdk: '^3.0.0').

• Records: Records are anonymous immutable data structures that let you aggregate multiple values together, similar to tuples in other languages. With records, you can return multiple values from a function, create composite map keys, or use them any other place where you want to bundle a couple of objects together.

  For example, using a record to return two values:

  (double x, double y) geoLocation(String name) {
    if (name == 'Nairobi') {
      return (-1.2921, 36.8219);
    } else {
      ...
    }
  }
  

• Pattern matching: Expressions build values out of smaller pieces. Conversely, patterns are an expressive tool for decomposing values back into their constituent parts. Patterns can call getters on an object, access elements from a list, pull fields out of a record, etc. For example, we can destructure the record from the previous example like so:

  var (lat, long) = geoLocation('Nairobi');
  print('Nairobi is at $lat, $long.');
  

  Patterns can also be used in switch cases. There, you can destructure values and also test them to see if they have a certain type or value:

  switch (object) {
    case [int a]:
      print('A list with a single integer element $a');
    case ('name', _):
      print('A two-element record whose first field is "name".');
    default: print('Some other object.');
  }
  

  Also, as you can see, non-empty switch cases no longer need break; statements.

  Breaking change: Dart 3.0 interprets switch cases as patterns instead of constant expressions. Most constant expressions found in switch cases are valid patterns with the same meaning (named constants, literals, etc.). You may need to tweak a few constant expressions to make them valid. This only affects libraries that have upgraded to language version 3.0.

• Switch expressions: Switch expressions allow you to use patterns and multi-way branching in contexts where a statement isn't allowed:

  return TextButton(
    onPressed: _goPrevious,
    child: Text(switch (page) {
      0 => 'Exit story',
      1 => 'First page',
      _ when page == _lastPage => 'Start over',
      _ => 'Previous page',
    }),
  );
  

• If-case statements and elements: A new if construct that matches a value against a pattern and executes the then or else branch depending on whether the pattern matches:

  if (json case ['user', var name]) {
    print('Got user message for user $name.');
  }
  

  There is also a corresponding if-case element that can be used in collection literals.

• Sealed classes: When you mark a type sealed, the compiler ensures that switches on values of that type exhaustively cover every subtype. This enables you to program in an algebraic datatype style with the compile-time safety you expect:

  sealed class Amigo {}
  class Lucky extends Amigo {}
  class Dusty extends Amigo {}
  class Ned extends Amigo {}
  
  String lastName(Amigo amigo) =>
      switch (amigo) {
        Lucky _ => 'Day',
        Ned _   => 'Nederlander',
      };
  

  In this last example, the compiler reports an error that the switch doesn't cover the subclass Dusty.

• Class modifiers: New modifiers final, interface, base, and mixin on class and mixin declarations let you control how the type can be used. By default, Dart is flexible in that a single class declaration can be used as an interface, a superclass, or even a mixin. This flexibility can make it harder to evolve an API over time without breaking users. We mostly keep the current flexible defaults, but these new modifiers give you finer-grained control over how the type can be used.

  Breaking change: Class declarations from libraries that have been upgraded to Dart 3.0 can no longer be used as mixins by default. If you want the class to be usable as both a class and a mixin, mark it mixin class. If you want it to be used only as a mixin, make it a mixin declaration. If you haven't upgraded a class to Dart 3.0, you can still use it as a mixin.

• Breaking change #50902: Dart reports a compile-time error if a continue statement targets a label that is not a loop (for, do and while statements) or a switch member. Fix this by changing the continue to target a valid labeled statement.

• Breaking change language/#2357: Starting in language version 3.0, Dart reports a compile-time error if a colon (:) is used as the separator before the default value of an optional named parameter. Fix this by changing the colon (:) to an equal sign (=).

Libraries

General changes

• Breaking Change: Non-mixin classes in the platform libraries can no longer be mixed in, unless they are explicitly marked as mixin class. The following existing classes have been made mixin classes:
  • Iterable
  • IterableMixin (now alias for Iterable)
  • IterableBase (now alias for Iterable)
  • ListMixin
  • SetMixin
  • MapMixin
  • LinkedListEntry
  • StringConversionSink

dart:core

• Added bool.parse and bool.tryParse static methods.

• Added DateTime.timestamp() constructor to get current time as UTC.

• The type of RegExpMatch.pattern is now RegExp, not just Pattern.

• Breaking change #49529:

  • Removed the deprecated List constructor, as it wasn't null safe. Use list literals (e.g. [] for an empty list or <int>[] for an empty typed list) or List.filled.
  • Removed the deprecated onError argument on int.parse, double.parse, and num.parse. Use the tryParse method instead.
  • Removed the deprecated proxy and Provisional annotations. The original proxy annotation has no effect in Dart 2, and the Provisional type and provisional constant were only used internally during the Dart 2.0 development process.
  • Removed the deprecated Deprecated.expires getter. Use Deprecated.message instead.
  • Removed the deprecated CastError error. Use TypeError instead.
  • Removed the deprecated FallThroughError error. The kind of fall-through previously throwing this error was made a compile-time error in Dart 2.0.
  • Removed the deprecated NullThrownError error. This error is never thrown from null safe code.
  • Removed the deprecated AbstractClassInstantiationError error. It was made a compile-time error to call the constructor of an abstract class in Dart 2.0.
  • Removed the deprecated CyclicInitializationError. Cyclic dependencies are no longer detected at runtime in null safe code. Such code will fail in other ways instead, possibly with a StackOverflowError.
  • Removed the deprecated NoSuchMethodError default constructor. Use the NoSuchMethodError.withInvocation named constructor instead.
  • Removed the deprecated BidirectionalIterator class. Existing bidirectional iterators can still work, they just don't have a shared supertype locking them to a specific name for moving backwards.

• Breaking change when migrating code to Dart 3.0: Some changes to platform libraries only affect code when that code is migrated to language version 3.0.

  • The Function type can no longer be implemented, extended or mixed in. Since Dart 2.0 writing implements Function has been allowed for backwards compatibility, but it has not had any effect. In Dart 3.0, the Function type is final and cannot be subtyped, preventing code from mistakenly assuming it works.

  • The following declarations can only be implemented, not extended:

    • Comparable
    • Exception
    • Iterator
    • Pattern
    • Match
    • RegExp
    • RegExpMatch
    • StackTrace
    • StringSink

    None of these declarations contained any implementation to inherit, and are marked as interface to signify that they are only intended as interfaces.

  • The following declarations can no longer be implemented or extended:

    • MapEntry
    • OutOfMemoryError
    • StackOverflowError
    • Expando
    • WeakReference
    • Finalizer

    The MapEntry value class is restricted to enable later optimizations. The remaining classes are tightly coupled to the platform and not intended to be subclassed or implemented.

dart:async

• Added extension member wait on iterables and 2-9 tuples of futures.

• Breaking change #49529:

  • Removed the deprecated DeferredLibrary class. Use the deferred as import syntax instead.

dart:collection

• Added extension members nonNulls, firstOrNull, lastOrNull, singleOrNull, elementAtOrNull and indexed on Iterables. Also exported from dart:core.

• Deprecated the HasNextIterator class (#50883).

• Breaking change when migrating code to Dart 3.0: Some changes to platform libraries only affect code when it is migrated to language version 3.0.

  • The following interface can no longer be extended, only implemented:
    • Queue
  • The following implementation classes can no longer be implemented:
    • LinkedList
    • LinkedListEntry
  • The following implementation classes can no longer be implemented or extended:
    • HasNextIterator (Also deprecated.)
    • HashMap
    • LinkedHashMap
    • HashSet
    • LinkedHashSet
    • DoubleLinkedQueue
    • ListQueue
    • SplayTreeMap
    • SplayTreeSet

dart:developer

• Breaking change #49529:

  • Removed the deprecated MAX_USER_TAGS constant. Use maxUserTags instead.

• Callbacks passed to registerExtension will be run in the zone from which they are registered.

• Breaking change #50231:

  • Removed the deprecated Metrics, Metric, Counter, and Gauge classes as they have been broken since Dart 2.0.

dart:ffi

• The experimental @FfiNative annotation is now deprecated. Usages should be replaced with the new @Native annotation.

dart:html

• Breaking change: As previously announced, the deprecated registerElement and registerElement2 methods in Document and HtmlDocument have been removed. See #49536 for details.

dart:math

• Breaking change when migrating code to Dart 3.0: Some changes to platform libraries only affect code when it is migrated to language version 3.0.
  • The Random interface can only be implemented, not extended.

dart:io

• Added name and signalNumber to the ProcessSignal class.
• Deprecate NetworkInterface.listSupported. Has always returned true since Dart 2.3.
• Finalize httpEnableTimelineLogging parameter name transition from enable to enabled. See #43638.
• Favor IPv4 connections over IPv6 when connecting sockets. See #50868.
• Breaking change #51035:
  • Update NetworkProfiling to accommodate new String ids that are introduced in vm_service:11.0.0

dart:js_util

• Added several helper functions to access more JavaScript operators, like delete and the typeof functionality.
• jsify is now permissive and has inverse semantics to dartify.
• jsify and dartify both handle types they understand natively more efficiently.
• Signature of callMethod has been aligned with the other methods and now takes Object instead of String.

Tools

Observatory

• Observatory is no longer served by default and users should instead use Dart DevTools. Users requiring specific functionality in Observatory should set the --serve-observatory flag.

Web Dev Compiler (DDC)

• Removed deprecated command line flags -k, --kernel, and --dart-sdk.
• The compile time flag --nativeNonNullAsserts, which ensures web library APIs are sound in their nullability, is by default set to true in sound mode. For more information on the flag, see NATIVE_NULL_ASSERTIONS.md.

dart2js

• The compile time flag --native-null-assertions, which ensures web library APIs are sound in their nullability, is by default set to true in sound mode, unless -O3 or higher is passed, in which case they are not checked. For more information on the flag, see NATIVE_NULL_ASSERTIONS.md.

Dart2js

• Cleanup related to #46100: the internal dart2js snapshot fails unless it is called from a supported interface, such as dart compile js, flutter build, or build_web_compilers. This is not expected to be a visible change.

Formatter

• Format sync* and async* functions with => bodies.
• Don't split after < in collection literals.
• Better indentation of multiline function types inside type argument lists.
• Fix bug where parameter metadata wouldn't always split when it should.

Analyzer

• Most static analysis "hints" are converted to be "warnings," and any remaining hints are intended to be converted soon after the Dart 3.0 release. This means that any (previously) hints reported by dart analyze are now considered "fatal" (will result in a non-zero exit code). The previous behavior, where such hints (now warnings) are not fatal, can be achieved by using the --no-fatal-warnings flag. This behavior can also be altered, on a code-by-code basis, by changing the severity of rules in an analysis options file.
• Add static enforcement of the SDK-only @Since annotation. When code in a package uses a Dart SDK element annotated with @Since, analyzer will report a warning if the package's Dart SDK constraint allows versions of Dart which don't include that element.
• Protects the Dart Analysis Server against extreme memory usage by limiting the number of plugins per analysis context to 1. (issue [#50981][]).

Linter

Updates the Linter to 1.35.0, which includes changes that

• add new lints:
  • implicit_reopen
  • unnecessary_breaks
  • type_literal_in_constant_pattern
  • invalid_case_patterns
• update existing lints to support patterns and class modifiers
• remove support for:
  • enable_null_safety
  • invariant_booleans
  • prefer_bool_in_asserts
  • prefer_equal_for_default_values
  • super_goes_last
• fix unnecessary_parenthesis false-positives with null-aware expressions.
• fix void_checks to allow assignments of Future<dynamic>? to parameters typed FutureOr<void>?.
• fix use_build_context_synchronously in if conditions.
• fix a false positive for avoid_private_typedef_functions with generalized type aliases.
• update unnecessary_parenthesis to detect some doubled parens.
• update void_checks to allow returning Never as void.
• update no_adjacent_strings_in_list to support set literals and for- and if-elements.
• update avoid_types_as_parameter_names to handle type variables.
• update avoid_positional_boolean_parameters to handle typedefs.
• update avoid_redundant_argument_values to check parameters of redirecting constructors.
• improve performance for prefer_const_literals_to_create_immutables.
• update use_build_context_synchronously to check context properties.
• improve unnecessary_parenthesis support for property accesses and method invocations.
• update unnecessary_parenthesis to allow parentheses in more null-aware cascade contexts.
• update unreachable_from_main to track static elements.
• update unnecessary_null_checks to not report on arguments passed to Future.value or Completer.complete.
• mark always_use_package_imports and prefer_relative_imports as incompatible rules.
• update only_throw_errors to not report on Never-typed expressions.
• update unnecessary_lambdas to not report with late final variables.
• update avoid_function_literals_in_foreach_calls to not report with nullable- typed targets.
• add new lint: deprecated_member_use_from_same_package which replaces the soft-deprecated analyzer hint of the same name.
• update public_member_api_docs to not require docs on enum constructors.
• update prefer_void_to_null to not report on as-expressions.

Migration tool removal

The null safety migration tool (dart migrate) has been removed. If you still have code which needs to be migrated to null safety, please run dart migrate using Dart version 2.19, before upgrading to Dart version 3.0.

Pub

• To preserve compatibility with null-safe code pre Dart 3, Pub will interpret a language constraint indicating a language version of 2.12 or higher and an upper bound of <3.0.0 as <4.0.0.

  For example >=2.19.2 <3.0.0 will be interpreted as >=2.19.2 <4.0.0.

• dart pub publish will no longer warn about dependency_overrides. Dependency overrides only take effect in the root package of a resolution.

• dart pub token add now verifies that the given token is valid for including in a header according to RFC 6750 section 2.1. This means they must contain only the characters: ^[a-zA-Z0-9._~+/=-]+$. Before a failure would happen when attempting to send the authorization header.

• dart pub get and related commands will now by default also update the dependencies in the example folder (if it exists). Use --no-example to avoid this.

• On Windows the PUB_CACHE has moved to %LOCALAPPDATA%, since Dart 2.8 the PUB_CACHE has been created in %LOCALAPPDATA% when one wasn't present. Hence, this only affects users with a PUB_CACHE created by Dart 2.7 or earlier. If you have path/to/.pub-cache/bin in PATH you may need to update your PATH.

• Added ConnectedAppService to store the connections to Dart and Flutter applications that DTD is aware of.
• Log exceptions from invalid streamNotify events.
• Added getRegisteredServices API.
• Added new response types RegisteredServicesResponse and VmServicesResponse.
• Breaking Change: Changed the serviceName parameter for the DartToolingDaemon.call method to have type String? instead of String.
• Breaking Change: When the params parameter for the DartToolingDaemon.call method is null, pass the null value along to the client peer request instead of sending an empty Map value.

This is a patch release that prevents type inference failures in the analyzer (Issue 38365).

• Widen the dependency on unified_analytics to include 8.0.0.

Language

The set of operations allowed in constant expressions has been expanded as described in the constant update proposal. The control flow and spread collection features shipped in Dart 2.3 are now also supported in constants as described in the specification here.

Specifically, it is now valid to use the following operations in constant expressions under the appropriate conditions:

• Casts (e as T) and type tests (e is T).
• Comparisons to null, even for types which override the == operator.
• The &, |, and ^ binary operators on booleans.
• The spread operators (... and ...?).
• An if element in a collection literal.

// Example: these are now valid constants.
const Object i = 3;
const list = [i as int];
const set = {if (list is List<int>) ...list};
const map = {if (i is int) i : "int"};

In addition, the semantics of constant evaluation has been changed as follows:

• The && operator only evaluates its second operand if the first evaluates to true.
• The || operator only evaluates its second operand if the first evaluates to false.
• The ?? operator only evaluates its second operand if the first evaluates to null.
• The conditional operator (e ? e1 : e2) only evaluates one of the two branches, depending on the value of the first operand.

// Example: x is now a valid constant definition.
const String s = null;
const int x = (s == null) ? 0 : s.length;

Core libraries

• Breaking change #36900: The following methods and properties across various core libraries, which used to declare a return type of List<int>, were updated to declare a return type of Uint8List:

  • BytesBuilder.takeBytes()
  • BytesBuilder.toBytes()
  • Datagram.data
  • File.readAsBytes() (Future<Uint8List>)
  • File.readAsBytesSync()
  • InternetAddress.rawAddress
  • RandomAccessFile.read() (Future<Uint8List>)
  • RandomAccessFile.readSync()
  • RawSocket.read()
  • Utf8Codec.encode() (and Utf8Encoder.convert())

  In addition, the following classes were updated to implement Stream<Uint8List> rather than Stream<List<int>>:

  • HttpRequest
  • Socket

  Possible errors and how to fix them

  • The argument type 'Utf8Decoder' can't be assigned to the parameter type 'StreamTransformer<Uint8List, dynamic>'

    type 'Utf8Decoder' is not a subtype of type 'StreamTransformer' of 'streamTransformer'"

    You can fix these call sites by updating your code to use StreamTransformer.bind() instead of Stream.transform(), like so:

    Before: stream.transform(utf8.decoder) After: utf8.decoder.bind(stream)

  • The argument type 'IOSink' can't be assigned to the parameter type 'StreamConsumer<Uint8List>'

    type '_IOSinkImpl' is not a subtype of type 'StreamConsumer<Uint8List>' of 'streamConsumer'

    You can fix these call sites by casting your stream instance to a Stream<List<int>> before calling .pipe() on the stream, like so:

    Before: stream.pipe(consumer) After: stream.cast<List<int>>().pipe(consumer)

  Finally, the following typed lists were updated to have their sublist() methods declare a return type that is the same as the source list:

  • Int8List.sublist() → Int8List
  • Int16List.sublist() → Int16List
  • Int32List.sublist() → Int32List
  • Int64List.sublist() → Int64List
  • Int32x4List.sublist() → Int32x4List
  • Float32List.sublist() → Float32List
  • Float64List.sublist() → Float64List
  • Float32x4List.sublist() → Float32x4List
  • Float64x2List.sublist() → Float64x2List
  • Uint8List.sublist() → Uint8List
  • Uint8ClampedList.sublist() → Uint8ClampedList
  • Uint16List.sublist() → Uint16List
  • Uint32List.sublist() → Uint32List
  • Uint64List.sublist() → Uint64List

dart:async

• Add value and error constructors on Stream to allow easily creating single-value or single-error streams.

dart:core

• Update Uri class to support RFC6874: "%25" or "%" can be appended to the end of a valid IPv6 representing a Zone Identifier. A valid zone ID consists of unreversed character or Percent encoded octet, which was defined in RFC3986. IPv6addrz = IPv6address "%25" ZoneID

dart:io

• Breaking change #37192: The Cookie class's constructor's name and value optional positional parameters are now mandatory. The signature changes from:

  Cookie([String name, String value])
  

  to

  Cookie(String name, String value)
  

  However, it has not been possible to set name and value to null since Dart 1.3.0 (2014) where a bug made it impossible. Any code not using both parameters or setting any to null would necessarily get a noSuchMethod exception at runtime. This change catches such erroneous uses at compile time. Since code could not previously correctly omit the parameters, this is not really a breaking change.

• Breaking change #37192: The Cookie class's name and value setters now validates that the strings are made from the allowed character set and are not null. The constructor already made these checks and this fixes the loophole where the setters didn't also validate.

Dart VM

Tools

Pub

• Clean-up invalid git repositories in cache when fetching from git.
• Breaking change #36765: Packages published to pub.dev can no longer contain git dependencies. These packages will be rejected by the server.

Linter

The Linter was updated to 0.1.96, which includes:

• fixed false positives in unnecessary_parens
• various changes to migrate to preferred analyzer APIs
• rule test fixes

Dartdoc

Dartdoc was updated to 0.28.4; this version includes several fixes and is based on a newer version of the analyzer package.

• Update SDK constraints to ^3.5.0.
• Add isClosed getter to DartToolingDaemon.

Core libraries

dart:isolate

• TransferableTypedData class was added to facilitate faster cross-isolate communication of Uint8List data.

• Breaking change: Isolate.resolvePackageUri will always throw an UnsupportedError when compiled with dart2js or DDC. This was the only remaining API in dart:isolate that didn't automatically throw since we dropped support for this library in Dart 2.0.0. Note that the API already throws in dart2js if the API is used directly without manually setting up a defaultPackagesBase hook.

dart:developer

• Exposed result, errorCode and errorDetail getters in ServiceExtensionResponse to allow for better debugging of VM service extension RPC results.

dart:io

• Fixed Cookie class interoperability with certain websites by allowing the cookie values to be the empty string (Issue 35804) and not stripping double quotes from the value (Issue 33327) in accordance with RFC 6265.

• #36971: The HttpClientResponse interface has been extended with the addition of a new compressionState getter, which specifies whether the body of a response was compressed when it was received and whether it has been automatically uncompressed via HttpClient.autoUncompress.

  As part of this change, a corresponding new enum was added to dart:io: HttpClientResponseCompressionState.

  This is a breaking change for those implementing the HttpClientResponse interface as subclasses will need to implement the new getter.

dart:async

• Breaking change #36382: The await for allowed null as a stream due to a bug in StreamIterator class. This bug has now been fixed.

dart:core

• #36171: The RegExp interface has been extended with two new constructor named parameters:

  • unicode: (bool, default: false), for Unicode patterns
  • dotAll: (bool, default: false), to change the matching behavior of '.' to also match line terminating characters.

  Appropriate properties for these named parameters have also been added so their use can be detected after construction.

  In addition, RegExp methods that originally returned Match objects now return a more specific subtype, RegExpMatch, which adds two features:

  • Iterable<String> groupNames, a property that contains the names of all named capture groups
  • String namedGroup(String name), a method that retrieves the match for the given named capture group

  This is a breaking change for implementers of the RegExp interface. Subclasses will need to add the new properties and may have to update the return types on overridden methods.

Language

• Breaking change #35097: Covariance of type variables used in super-interfaces is now enforced. For example, the following code was previously accepted and will now be rejected:

class A<X> {};
class B<X> extends A<void Function(X)> {};

• The identifier async can now be used in asynchronous and generator functions.

Dart for the Web

Dart Dev Compiler (DDC)

• Improve NoSuchMethod errors for failing dynamic calls. Now they include specific information about the nature of the error such as:
  • Attempting to call a null value.
  • Calling an object instance with a null call() method.
  • Passing too few or too many arguments.
  • Passing incorrect named arguments.
  • Passing too few or too many type arguments.
  • Passing type arguments to a non-generic method.

Tools

Linter

The Linter was updated to 0.1.91, which includes the following changes:

• Fixed missed cases in prefer_const_constructors
• Fixed prefer_initializing_formals to no longer suggest API breaking changes
• Updated omit_local_variable_types to allow explicit dynamics
• Fixed null-reference in unrelated_type_equality_checks
• New lint: unsafe_html
• Broadened prefer_null_aware_operators to work beyond local variables.
• Added prefer_if_null_operators.
• Fixed prefer_contains false positives.
• Fixed unnecessary_parenthesis false positives.
• Fixed prefer_asserts_in_initializer_lists false positives
• Fixed curly_braces_in_flow_control_structures to handle more cases
• New lint: prefer_double_quotes
• New lint: sort_child_properties_last
• Fixed type_annotate_public_apis false positive for static const initializers

Pub

• pub publish will no longer warn about missing dependencies for import statements in example/.
• OAuth2 authentication will explicitly ask for the openid scope.

• Bump unified_analytics dependency to ^7.0.0.

The focus in this release is on the new "UI-as-code" language features which make collections more expressive and declarative.

Language

Flutter is growing rapidly, which means many Dart users are building UI in code out of big deeply-nested expressions. Our goal with 2.3.0 was to make that kind of code easier to write and maintain. Collection literals are a large component, so we focused on three features to make collections more powerful. We'll use list literals in the examples below, but these features also work in map and set literals.

Spread

Placing ... before an expression inside a collection literal unpacks the result of the expression and inserts its elements directly inside the new collection. Where before you had to write something like this:

CupertinoPageScaffold(
  child: ListView(children: [
    Tab2Header()
  ]..addAll(buildTab2Conversation())
    ..add(buildFooter())),
);

Now you can write this:

CupertinoPageScaffold(
  child: ListView(children: [
    Tab2Header(),
    ...buildTab2Conversation(),
    buildFooter()
  ]),
);

If you know the expression might evaluate to null and you want to treat that as equivalent to zero elements, you can use the null-aware spread ...?.

Collection if

Sometimes you might want to include one or more elements in a collection only under certain conditions. If you're lucky, you can use a ?: operator to selectively swap out a single element, but if you want to exchange more than one or omit elements, you are forced to write imperative code like this:

Widget build(BuildContext context) {
  var children = [
    IconButton(icon: Icon(Icons.menu)),
    Expanded(child: title)
  ];

  if (isAndroid) {
    children.add(IconButton(icon: Icon(Icons.search)));
  }

  return Row(children: children);
}

We now allow if inside collection literals to conditionally omit or (with else) swap out an element:

Widget build(BuildContext context) {
  return Row(
    children: [
      IconButton(icon: Icon(Icons.menu)),
      Expanded(child: title),
      if (isAndroid)
        IconButton(icon: Icon(Icons.search)),
    ],
  );
}

Unlike the existing ?: operator, a collection if can be composed with spreads to conditionally include or omit multiple items:

Widget build(BuildContext context) {
  return Row(
    children: [
      IconButton(icon: Icon(Icons.menu)),
      if (isAndroid) ...[
        Expanded(child: title),
        IconButton(icon: Icon(Icons.search)),
      ]
    ],
  );
}

Collection for

In many cases, the higher-order methods on Iterable give you a declarative way to modify a collection in the context of a single expression. But some operations, especially involving both transforming and filtering, can be cumbersome to express in a functional style.

To solve this problem, you can use for inside a collection literal. Each iteration of the loop produces an element which is then inserted in the resulting collection. Consider the following code:

var command = [
  engineDartPath,
  frontendServer,
  ...fileSystemRoots.map((root) => "--filesystem-root=$root"),
  ...entryPoints
      .where((entryPoint) => fileExists("lib/$entryPoint.json"))
      .map((entryPoint) => "lib/$entryPoint"),
  mainPath
];

With a collection for, the code becomes simpler:

var command = [
  engineDartPath,
  frontendServer,
  for (var root in fileSystemRoots) "--filesystem-root=$root",
  for (var entryPoint in entryPoints)
    if (fileExists("lib/$entryPoint.json")) "lib/$entryPoint",
  mainPath
];

As you can see, all three of these features can be freely composed. For full details of the changes, see the official proposal.

Note: These features are not currently supported in const collection literals. In a future release, we intend to relax this restriction and allow spread and collection if inside const collections.

Core library changes

dart:isolate

• Added debugName property to Isolate.
• Added debugName optional parameter to Isolate.spawn and Isolate.spawnUri.

dart:core

• RegExp patterns can now use lookbehind assertions.
• RegExp patterns can now use named capture groups and named backreferences. Currently, named group matches can only be retrieved in Dart either by the implicit index of the named group or by downcasting the returned Match object to the type RegExpMatch. The RegExpMatch interface contains methods for retrieving the available group names and retrieving a match by group name.

Dart VM

• The VM service now requires an authentication code by default. This behavior can be disabled by providing the --disable-service-auth-codes flag.

• Support for deprecated flags '-c' and '--checked' has been removed.

Dart for the Web

dart2js

A binary format was added to dump-info. The old JSON format is still available and provided by default, but we are starting to deprecate it. The new binary format is more compact and cheaper to generate. On some large apps we tested, it was 4x faster to serialize and used 6x less memory.

To use the binary format today, use --dump-info=binary, instead of --dump-info.

What to expect next?

• The visualizer tool will not be updated to support the new binary format, but you can find several command-line tools at package:dart2js_info that provide similar features to those in the visualizer.

• The command-line tools in package:dart2js_info also work with the old JSON format, so you can start using them even before you enable the new format.

• In a future release --dump-info will default to --dump-info=binary. At that point, there will be an option to fallback to the JSON format, but the visualizer tool will be deprecated.

• A release after that, the JSON format will no longer be available from dart2js, but may be available from a command-line tool in package:dart2js_info.

Tools

dartfmt

• Tweak set literal formatting to follow other collection literals.
• Add support for "UI as code" features.
• Properly format trailing commas in assertions.
• Improve indentation of adjacent strings in argument lists.

Linter

The Linter was updated to 0.1.86, which includes the following changes:

• Added the following lints: prefer_inlined_adds, prefer_for_elements_to_map_fromIterable, prefer_if_elements_to_conditional_expressions, diagnostic_describe_all_properties.
• Updated file_names to skip prefixed-extension Dart files (.css.dart, .g.dart, etc.).
• Fixed false positives in unnecessary_parenthesis.

Pub

• Added a CHANGELOG validator that complains if you pub publish without mentioning the current version.
• Removed validation of library names when doing pub publish.
• Added support for pub global activateing package from a custom pub URL.
• Added subcommand: pub logout. Logs you out of the current session.

Dart native

Initial support for compiling Dart apps to native machine code has been added. Two new tools have been added to the bin folder of the Dart SDK:

• dart2aot: AOT (ahead-of-time) compiles a Dart program to native machine code. The tool is supported on Windows, macOS, and Linux.

• dartaotruntime: A small runtime used for executing an AOT compiled program.

• Indicate compatibility with package:web_socket_channel 2.x and 3.x.
• Bump minimum version for package:unified_analytics to 6.1.0.
• DartToolingDaemon.connect will now wait for the web socket to be connected.
• The DartToolingDaemon constructor is now public and can be directly called with a StreamChannel<String>.
• The params parameter in DartToolingDaemon.call() has been changed from Map<String, Object>? to Map<String, Object?>?.
• registerService now allows passing a Map<String, Object?>? capabilities that can be supplied to clients via new ServiceRegistered and ServiceUregistered events on the Service stream (when connected to a version of DTD that supports these streams).
• Calling DartToolingDaemon.onEvent() now returns a broadcast stream. This means multiple listeners can be added, but also means you must add a listener prior to calling streamListen to avoid the possibility of missing events.

Language

Sets now have a literal syntax like lists and maps do:

var set = {1, 2, 3};

Using curly braces makes empty sets ambiguous with maps:

var collection = {}; // Empty set or map?

To avoid breaking existing code, an ambiguous literal is treated as a map. To create an empty set, you can rely on either a surrounding context type or an explicit type argument:

// Variable type forces this to be a set:
Set<int> set = {};

// A single type argument means this must be a set:
var set2 = <int>{};

Set literals are released on all platforms. The set-literals experiment flag has been disabled.

Tools

Analyzer

• The DEPRECATED_MEMBER_USE hint was split into two hints:

  • DEPRECATED_MEMBER_USE reports on usage of @deprecated members declared in a different package.
  • DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE reports on usage of @deprecated members declared in the same package.

Linter

Upgraded the linter to 0.1.82 which adds the following improvements:

• Added provide_deprecation_message, and use_full_hex_values_for_flutter_colors, prefer_null_aware_operators.
• Fixed prefer_const_declarations set literal false-positives.
• Updated prefer_collection_literals to support set literals.
• Updated unnecessary_parenthesis play nicer with cascades.
• Removed deprecated lints from the "all options" sample.
• Stopped registering "default lints".
• Fixed hash_and_equals to respect hashCode fields.

Other libraries

package:kernel

• Breaking change: The klass getter on the InstanceConstant class in the Kernel AST API has been renamed to classNode for consistency.

• Breaking change: Updated Link implementation to utilize true symbolic links instead of junctions on Windows. Existing junctions will continue to work with the new Link implementation, but all new links will create symbolic links.

  To create a symbolic link, Dart must be run with administrative privileges or Developer Mode must be enabled, otherwise a FileSystemException will be raised with errno set to ERROR_PRIVILEGE_NOT_HELD (Issue 33966).

• Added new response types Success, StringResponse, BoolResponse, and StringListResponse.
• Added contributing guide (CONTRIBUTING.md).

This is a minor version release. The team's focus was mostly on improving performance and stability after the large changes in Dart 2.0.0. Notable changes:

• We've introduced a dedicated syntax for declaring a mixin. Instead of the class keyword, it uses mixin:

  mixin SetMixin<E> implements Set<E> {
    ...
  }
  

  The new syntax also enables super calls inside mixins.

• Integer literals now work in double contexts. When passing a literal number to a function that expects a double, you no longer need an explicit .0 at the end of the number. In releases before 2.1, you need code like this when setting a double like fontSize:

  TextStyle(fontSize: 18.0)
  

  Now you can remove the .0:

  TextStyle(fontSize: 18)
  

  In releases before 2.1, fontSize : 18 causes a static error. This was a common mistake and source of friction.

• Breaking change: A number of static errors that should have been detected and reported were not supported in 2.0.0. These are reported now, which means existing incorrect code may show new errors.

• dart:core now exports Future and Stream. You no longer need to import dart:async to use those very common types.

Language

• Introduced a new syntax for mixin declarations.

  mixin SetMixin<E> implements Set<E> {
    ...
  }
  

  Most classes that are intended to be used as mixins are intended to only be used as mixins. The library author doesn't want users to be able to construct or subclass the class. The new syntax makes that intent clear and enforces it in the type system. It is an error to extend or construct a type declared using mixin. (You can implement it since mixins expose an implicit interface.)

  Over time, we expect most mixin declarations to use the new syntax. However, if you have a "mixin" class where users are extending or constructing it, note that moving it to the new syntax is a breaking API change since it prevents users from doing that. If you have a type like this that is a mixin as well as being a concrete class and/or superclass, then the existing syntax is what you want.

  If you need to use a super inside a mixin, the new syntax is required. This was previously only allowed with the experimental --supermixins flag because it has some complex interactions with the type system. The new syntax addresses those issues and lets you use super calls by declaring the superclass constraint your mixin requires:

  class Superclass {
    superclassMethod() {
      print("in superclass");
    }
  }
  
  mixin SomeMixin on Superclass {
    mixinMethod() {
      // This is OK:
      super.superclassMethod();
    }
  }
  
  class GoodSub extends Superclass with SomeMixin {}
  
  class BadSub extends Object with SomeMixin {}
  // Error: Since the super() call in mixinMethod() can't find a
  // superclassMethod() to call, this is prohibited.
  

  Even if you don't need to use super calls, the new mixin syntax is good because it clearly expresses that you intend the type to be mixed in.

• Allow integer literals to be used in double contexts. An integer literal used in a place where a double is required is now interpreted as a double value. The numerical value of the literal needs to be precisely representable as a double value.

• Integer literals compiled to JavaScript are now allowed to have any value that can be exactly represented as a JavaScript Number. They were previously limited to such numbers that were also representable as signed 64-bit integers.

(Breaking) A number of static errors that should have been detected and reported were not supported in 2.0.0. These are reported now, which means existing incorrect code may show new errors:

• Setters with the same name as the enclosing class aren't allowed. (Issue 34225.) It is not allowed to have a class member with the same name as the enclosing class:

  class A {
    set A(int x) {}
  }
  

  Dart 2.0.0 incorrectly allows this for setters (only). Dart 2.1.0 rejects it.

  To fix: This is unlikely to break anything, since it violates all style guides anyway.

• Constant constructors cannot redirect to non-constant constructors. (Issue 34161.) It is not allowed to have a constant constructor that redirects to a non-constant constructor:

  class A {
    const A.foo() : this(); // Redirecting to A()
    A() {}
  }
  

  Dart 2.0.0 incorrectly allows this. Dart 2.1.0 rejects it.

  To fix: Make the target of the redirection a properly const constructor.

• Abstract methods may not unsoundly override a concrete method. (Issue 32014.) Concrete methods must be valid implementations of their interfaces:

  class A {
    num get thing => 2.0;
  }
  
  abstract class B implements A {
    int get thing;
  }
  
  class C extends A with B {}
  // 'thing' from 'A' is not a valid override of 'thing' from 'B'.
  
  main() {
    print(new C().thing.isEven); // Expects an int but gets a double.
  }
  

  Dart 2.0.0 allows unsound overrides like the above in some cases. Dart 2.1.0 rejects them.

  To fix: Relax the type of the invalid override, or tighten the type of the overridden method.

• Classes can't implement FutureOr. (Issue 33744.) Dart doesn't allow classes to implement the FutureOr type:

  class A implements FutureOr<Object> {}
  

  Dart 2.0.0 allows classes to implement FutureOr. Dart 2.1.0 does not.

  To fix: Don't do this.

• Type arguments to generic typedefs must satisfy their bounds. (Issue 33308.) If a parameterized typedef specifies a bound, actual arguments must be checked against it:

  class A<X extends int> {}
  
  typedef F<Y extends int> = A<Y> Function();
  
  F<num> f = null;
  

  Dart 2.0.0 allows bounds violations like F<num> above. Dart 2.1.0 rejects them.

  To fix: Either remove the bound on the typedef parameter, or pass a valid argument to the typedef.

• Constructor invocations must use valid syntax, even with optional new. (Issue 34403.) Type arguments to generic named constructors go after the class name, not the constructor name, even when used without an explicit new:

  class A<T> {
    A.foo() {}
  }
  
  main() {
    A.foo<String>(); // Incorrect syntax, was accepted in 2.0.0.
    A<String>.foo(); // Correct syntax.
  }
  

  Dart 2.0.0 accepts the incorrect syntax when the new keyword is left out. Dart 2.1.0 correctly rejects this code.

  To fix: Move the type argument to the correct position after the class name.

• Instance members should shadow prefixes. (Issue 34498.) If the same name is used as an import prefix and as a class member name, then the class member name takes precedence in the class scope.

  import 'dart:core';
  import 'dart:core' as core;
  
  class A {
    core.List get core => null; // "core" refers to field, not prefix.
  }
  

  Dart 2.0.0 incorrectly resolves the use of core in core.List to the prefix name. Dart 2.1.0 correctly resolves this to the field name.

  To fix: Change the prefix name to something which does not clash with the instance member.

• Implicit type arguments in extends clauses must satisfy the class bounds. (Issue 34532.) Implicit type arguments for generic classes are computed if not passed explicitly, but when used in an extends clause they must be checked for validity:

  class Foo<T> {}
  
  class Bar<T extends Foo<T>> {}
  
  class Baz extends Bar {} // Should error because Bar completes to Bar<Foo>
  

  Dart 2.0.0 accepts the broken code above. Dart 2.1.0 rejects it.

  To fix: Provide explicit type arguments to the superclass that satisfy the bound for the superclass.

• Mixins must correctly override their superclasses. (Issue 34235.) In some rare cases, combinations of uses of mixins could result in invalid overrides not being caught:

  class A {
    num get thing => 2.0;
  }
  
  class M1 {
    int get thing => 2;
  }
  
  class B = A with M1;
  
  class M2 {
    num get thing => 2.0;
  }
  
  class C extends B with M2 {} // 'thing' from 'M2' not a valid override.
  
  main() {
    M1 a = new C();
    print(a.thing.isEven); // Expects an int but gets a double.
  }
  

  Dart 2.0.0 accepts the above example. Dart 2.1.0 rejects it.

  To fix: Ensure that overriding methods are correct overrides of their superclasses, either by relaxing the superclass type, or tightening the subclass/mixin type.

Core libraries

dart:async

• Fixed a bug where calling stream.take(0).drain(value) would not correctly forward the value through the returned Future.
• Added a StreamTransformer.fromBind constructor.
• Updated Stream.fromIterable to send a done event after the error when the iterator's moveNext throws, and handle if the current getter throws (issue 33431).

dart:core

• Added HashMap.fromEntries and LinkedHashmap.fromEntries constructors.
• Added ArgumentError.checkNotNull utility method.
• Made Uri parsing more permissive about [ and ] occurring in the path, query or fragment, and # occurring in fragment.
• Exported Future and Stream from dart:core.
• Added operators &, | and ^ to bool.
• Added missing methods to UnmodifiableMapMixin. Some maps intended to be unmodifiable incorrectly allowed new methods added in Dart 2 to succeed.
• Deprecated the provisional annotation and the Provisional annotation class. These should have been removed before releasing Dart 2.0, and they have no effect.

dart:html

Fixed Service Workers and any Promise/Future API with a Dictionary parameter.

APIs in dart:html (that take a Dictionary) will receive a Dart Map parameter. The Map parameter must be converted to a Dictionary before passing to the browser's API. Before this change, any Promise/Future API with a Map/Dictionary parameter never called the Promise and didn't return a Dart Future - now it does.

This caused a number of breaks especially in Service Workers (register, etc.). Here is a complete list of the fixed APIs:

• BackgroundFetchManager

  • Future<BackgroundFetchRegistration> fetch(String id, Object requests, [Map options])

• CacheStorage

  • Future match(/*RequestInfo*/ request, [Map options])

• CanMakePayment

  • Future<List<Client>> matchAll([Map options])

• CookieStore

  • Future getAll([Map options])
  • Future set(String name, String value, [Map options])

• CredentialsContainer

  • Future get([Map options])
  • Future create([Map options])

• ImageCapture

  • Future setOptions(Map photoSettings)

• MediaCapabilities

  • Future<MediaCapabilitiesInfo> decodingInfo(Map configuration)
  • Future<MediaCapabilitiesInfo> encodingInfo(Map configuration)

• MediaStreamTrack

  • Future applyConstraints([Map constraints])

• Navigator

  • Future requestKeyboardLock([List<String> keyCodes])
  • Future requestMidiAccess([Map options])
  • Future share([Map data])

• OffscreenCanvas

  • Future<Blob> convertToBlob([Map options])

• PaymentInstruments

  • Future set(String instrumentKey, Map details)

• Permissions

  • Future<PermissionStatus> query(Map permission)
  • Future<PermissionStatus> request(Map permissions)
  • Future<PermissionStatus> revoke(Map permission)

• PushManager

  • Future permissionState([Map options])
  • Future<PushSubscription> subscribe([Map options])

• RtcPeerConnection

  • Changed:

    Future createAnswer([options_OR_successCallback,
        RtcPeerConnectionErrorCallback failureCallback,
        Map mediaConstraints])
    

    to:

    Future<RtcSessionDescription> createAnswer([Map options])
    

  • Changed:

    Future createOffer([options_OR_successCallback,
        RtcPeerConnectionErrorCallback failureCallback,
        Map rtcOfferOptions])
    

    to:

    Future<RtcSessionDescription> createOffer([Map options])
    

  • Changed:

    Future setLocalDescription(Map description,
        VoidCallback successCallback,
        [RtcPeerConnectionErrorCallback failureCallback])
    

    to:

    Future setLocalDescription(Map description)
    

  • Changed:

    Future setLocalDescription(Map description,
        VoidCallback successCallback,
        [RtcPeerConnectionErrorCallback failureCallback])
    

    to:

    Future setRemoteDescription(Map description)
    

• ServiceWorkerContainer

  • Future<ServiceWorkerRegistration> register(String url, [Map options])

• ServiceWorkerRegistration

  • Future<List<Notification>> getNotifications([Map filter])
  • Future showNotification(String title, [Map options])

• VRDevice

  • Future requestSession([Map options])
  • Future supportsSession([Map options])

• VRSession

  • Future requestFrameOfReference(String type, [Map options])

• Window

  • Future fetch(/*RequestInfo*/ input, [Map init])

• WorkerGlobalScope

  • Future fetch(/*RequestInfo*/ input, [Map init])

In addition, exposed Service Worker "self" as a static getter named "instance". The instance is exposed on four different Service Worker classes and can throw a InstanceTypeError if the instance isn't of the class expected (WorkerGlobalScope.instance will always work and not throw):

• SharedWorkerGlobalScope.instance
• DedicatedWorkerGlobalScope.instance
• ServiceWorkerGlobalScope.instance
• WorkerGlobalScope.instance

dart:io

• Added new HTTP status codes.

Dart for the Web

dart2js

• (Breaking) Duplicate keys in a const map are not allowed and produce a compile-time error. Dart2js used to report this as a warning before. This was already an error in dartanalyzer and DDC and will be an error in other tools in the future as well.

• Added -O flag to tune optimization levels. For more details run dart2js -h -v.

  We recommend to enable optimizations using the -O flag instead of individual flags for each optimization. This is because the -O flag is intended to be stable and continue to work in future versions of dart2js, while individual flags may come and go.

  At this time we recommend to test and debug with -O1 and to deploy with -O3.

Tool Changes

dartfmt

• Addressed several dartfmt issues when used with the new CFE parser.

Linter

Bumped the linter to 0.1.70 which includes the following new lints:

• avoid_returning_null_for_void
• sort_pub_dependencies
• prefer_mixin
• avoid_implementing_value_types
• flutter_style_todos
• avoid_void_async
• prefer_void_to_null

and improvements:

• Fixed NPE in prefer_iterable_whereType.
• Improved message display for await_only_futures
• Performance improvements for null_closures
• Mixin support
• Updated sort_constructors_first to apply to all members.
• Updated unnecessary_this to work on field initializers.
• Updated unawaited_futures to ignore assignments within cascades.
• Improved handling of constant expressions with generic type params.
• NPE fix for invariant_booleans.
• Improved docs for unawaited_futures.
• Updated unawaited_futures to check cascades.
• Relaxed void_checks (allowing T Function() to be assigned to void Function()).
• Fixed false positives in lines_longer_than_80_chars.

Pub

• Renamed the --checked flag to pub run to --enable-asserts.
• Pub will no longer delete directories named "packages".
• The --packages-dir flag is now ignored.

• Added getProjectRoots API.
• Expose constant values from dtd.dart.

This is the first major version release of Dart since 1.0.0, so it contains many significant changes across all areas of the platform. Large changes include:

• (Breaking) The unsound optional static type system has been replaced with a sound static type system using type inference and runtime checks. This was formerly called "strong mode" and only used by the Dart for web products. Now it is the one official static type system for the entire platform and replaces the previous "checked" and "production" modes.

• (Breaking) Functions marked async now run synchronously until the first await statement. Previously, they would return to the event loop once at the top of the function body before any code runs (issue 30345).

• (Breaking) Constants in the core libraries have been renamed from SCREAMING_CAPS to lowerCamelCase.

• (Breaking) Many new methods have been added to core library classes. If you implement the interfaces of these classes, you will need to implement the new methods.

• (Breaking) "dart:isolate" and "dart:mirrors" are no longer supported when using Dart for the web. They are still supported in the command-line VM.

• (Breaking) Pub's transformer-based build system has been replaced by a new build system.

• The new keyword is optional and can be omitted. Likewise, const can be omitted inside a const context (issue 30921).

• Dartium is no longer maintained or supported.

Language

• "Strong mode" is now the official type system of the language.

• The new keyword is optional and can be omitted. Likewise, const can be omitted inside a const context.

• A string in a part of declaration may now be used to refer to the library this file is part of. A library part can now declare its library as either:

  part of name.of.library;
  

  Or:

  part of "uriReferenceOfLibrary.dart";
  

  This allows libraries with no library declarations (and therefore no name) to have parts, and it allows tools to easily find the library of a part file. The Dart 1.0 syntax is supported but deprecated.

• Functions marked async now run synchronously until the first await statement. Previously, they would return to the event loop once at the top of the function body before any code runs (issue 30345).

• The type void is now a Top type like dynamic, and Object. It also now has new errors for being used where not allowed (such as being assigned to any non-void-typed parameter). Some libraries (importantly, mockito) may need to be updated to accept void values to keep their APIs working.

• Future flattening is now done only as specified in the Dart 2.0 spec, rather than more broadly. This means that the following code has an error on the assignment to y.

  test() {
    Future<int> f;
    var x = f.then<Future<List<int>>>((x) => []);
    Future<List<int>> y = x;
  }
  

• Invocations of noSuchMethod() receive default values for optional args. The following program used to print "No arguments passed", and now prints "First argument is 3".

  abstract class B {
    void m([int x = 3]);
  }
  
  class A implements B {
    noSuchMethod(Invocation i) {
      if (i.positionalArguments.length == 0) {
        print("No arguments passed");
      } else {
        print("First argument is ${i.positionalArguments[0]}");
      }
    }
  }
  
  void main() {
    A().m();
  }
  

• Bounds on generic functions are invariant. The following program now issues an invalid override error (issue 29014):

  class A {
    void f<T extends int>() {}
  }
  
  class B extends A {
    @override
    void f<T extends num>() {}
  }
  

• Numerous corner case bugs around return statements in synchronous and asynchronous functions fixed. Specifically:

  • Issues 31887, 32881. Future flattening should not be recursive.
  • Issues 30638, 32233. Incorrect downcast errors with FutureOr.
  • Issue 32233. Errors when returning FutureOr.
  • Issue 33218. Returns in functions with void related types.
  • Issue 31278. Incorrect hint on empty returns in async. functions.

• An empty return; in an async function with return type Future<Object> does not report an error.

• return exp; where exp has type void in an async function is now an error unless the return type of the function is void or dynamic.

• Mixed return statements of the form return; and return exp; are now allowed when exp has type void.

• A compile time error is emitted for any literal which cannot be exactly represented on the target platform. As a result, dart2js and DDC report errors if an integer literal cannot be represented exactly in JavaScript (issue 33282).

• New member conflict rules have been implemented. Most cases of conflicting members with the same name are now static errors (issue 33235).

Core libraries

• Replaced UPPER_CASE constant names with lowerCamelCase. For example, HTML_ESCAPE is now htmlEscape.

• The Web libraries were re-generated using Chrome 63 WebIDLs (details).

dart:async

• Stream:
  • Added cast and castFrom.
  • Changed firstWhere, lastWhere, and singleWhere to return Future<T> and added an optional T orElse() callback.
• StreamTransformer: added cast and castFrom.
• StreamTransformerBase: new class.
• Timer: added tick property.
• Zone
  • changed to be strong-mode clean. This required some breaking API changes. See https://goo.gl/y9mW2x for more information.
  • Added bindBinaryCallbackGuarded, bindCallbackGuarded, and bindUnaryCallbackGuarded.
  • Renamed Zone.ROOT to Zone.root.
• Removed the deprecated defaultValue parameter on Stream.firstWhere and Stream.lastWhere.
• Changed an internal lazily-allocated reusable "null future" to always belong to the root zone. This avoids race conditions where the first access to the future determined which zone it would belong to. The zone is only used for scheduling the callback of listeners, the listeners themselves will run in the correct zone in any case. Issue #32556.

dart:cli

• New "provisional" library for CLI-specific features.
• waitFor: function that suspends a stack to wait for a Future to complete.

dart:collection

• MapBase: added mapToString.
• LinkedHashMap no longer implements HashMap
• LinkedHashSet no longer implements HashSet.
• Added of constructor to Queue, ListQueue, DoubleLinkedQueue, HashSet, LinkedHashSet, SplayTreeSet, Map, HashMap, LinkedHashMap, SplayTreeMap.
• Removed Maps class. Extend MapBase or mix in MapMixin instead to provide map method implementations for a class.
• Removed experimental Document method getCSSCanvasContext and property supportsCssCanvasContext.
• Removed obsolete Element property xtag no longer supported in browsers.
• Exposed ServiceWorker class.
• Added constructor to MessageChannel and MessagePort addEventListener automatically calls start method to receive queued messages.

dart:convert

• Base64Codec.decode return type is now Uint8List.
• JsonUnsupportedObjectError: added partialResult property
• LineSplitter now implements StreamTransformer<String, String> instead of Converter. It retains Converter methods convert and startChunkedConversion.
• Utf8Decoder when compiled with dart2js uses the browser's TextDecoder in some common cases for faster decoding.
• Renamed ASCII, BASE64, BASE64URI, JSON, LATIN1 and UTF8 to ascii, base64, base64Uri, json, latin1 and utf8.
• Renamed the HtmlEscapeMode constants UNKNOWN, ATTRIBUTE, SQ_ATTRIBUTE and ELEMENT to unknown, attribute, sqAttribute and elements.
• Added jsonEncode, jsonDecode, base64Encode, base64UrlEncode and base64Decode top-level functions.
• Changed return type of encode on AsciiCodec and Latin1Codec, and convert on AsciiEncoder, Latin1Encoder, to Uint8List.
• Allow utf8.decoder.fuse(json.decoder) to ignore leading Unicode BOM.

dart:core

• BigInt class added to support integers greater than 64-bits.
• Deprecated the proxy annotation.
• Added Provisional class and provisional field.
• Added pragma annotation.
• RegExp added static escape function.
• The Uri class now correctly handles paths while running on Node.js on Windows.
• Core collection changes:
  • Iterable added members cast, castFrom, followedBy and whereType.
  • Iterable.singleWhere added orElse parameter.
  • List added + operator, first and last setters, and indexWhere and lastIndexWhere methods, and static copyRange and writeIterable methods.
  • Map added fromEntries constructor.
  • Map added addEntries, cast, entries, map, removeWhere, update and updateAll members.
  • MapEntry: new class used by Map.entries.
  • Note: if a class extends IterableBase, ListBase, SetBase or MapBase (or uses the corresponding mixins) from dart:collection, the new members are implemented automatically.
  • Added of constructor to List, Set, Map.
• Renamed double.INFINITY, double.NEGATIVE_INFINITY, double.NAN, double.MAX_FINITE and double.MIN_POSITIVE to double.infinity, double.negativeInfinity, double.nan, double.maxFinite and double.minPositive.
• Renamed the following constants in DateTime to lower case: MONDAY through SUNDAY, DAYS_PER_WEEK (as daysPerWeek), JANUARY through DECEMBER and MONTHS_PER_YEAR (as monthsPerYear).
• Renamed the following constants in Duration to lower case: MICROSECONDS_PER_MILLISECOND to microsecondsPerMillisecond, MILLISECONDS_PER_SECOND to millisecondsPerSecond, SECONDS_PER_MINUTE to secondsPerMinute, MINUTES_PER_HOUR to minutesPerHour, HOURS_PER_DAY to hoursPerDay, MICROSECONDS_PER_SECOND to microsecondsPerSecond, MICROSECONDS_PER_MINUTE to microsecondsPerMinute, MICROSECONDS_PER_HOUR to microsecondsPerHour, MICROSECONDS_PER_DAY to microsecondsPerDay, MILLISECONDS_PER_MINUTE to millisecondsPerMinute, MILLISECONDS_PER_HOUR to millisecondsPerHour, MILLISECONDS_PER_DAY to millisecondsPerDay, SECONDS_PER_HOUR to secondsPerHour, SECONDS_PER_DAY to secondsPerDay, MINUTES_PER_DAY to minutesPerDay, and ZERO to zero.
• Added typeArguments to Invocation class.
• Added constructors to invocation class that allows creation of Invocation objects directly, without going through noSuchMethod.
• Added unaryMinus and empty constant symbols on the Symbol class.
• Changed return type of UriData.dataAsBytes to Uint8List.
• Added tryParse static method to int, double, num, BigInt, Uri and DateTime.
• Deprecated onError parameter on int.parse, double.parse and num.parse.
• Deprecated the NoSuchMethodError constructor.
• int.parse on the VM no longer accepts unsigned hexadecimal numbers greater than or equal to 2**63 when not prefixed by 0x. (SDK issue 32858)

dart:developer

• Flow class added.
• Timeline.startSync and Timeline.timeSync now accepts an optional parameter flow of type Flow. The flow parameter is used to generate flow timeline events that are enclosed by the slice described by Timeline.{start,finish}Sync and Timeline.timeSync.

<!-- Still need entries for all changes to dart:html since 1.x -->

dart:html

• Removed deprecated query and queryAll. Use querySelector and querySelectorAll.

dart:io

• HttpStatus added UPGRADE_REQUIRED.
• IOOverrides and HttpOverrides added to aid in writing tests that wish to mock varios dart:io objects.
• Platform.operatingSystemVersion added that gives a platform-specific String describing the version of the operating system.
• ProcessStartMode.INHERIT_STDIO added, which allows a child process to inherit the parent's stdio handles.
• RawZLibFilter added for low-level access to compression and decompression routines.
• Unified backends for SecureSocket, SecurityContext, and X509Certificate to be consistent across all platforms. All SecureSocket, SecurityContext, and X509Certificate properties and methods are now supported on iOS and OSX.
• SecurityContext.alpnSupported deprecated as ALPN is now supported on all platforms.
• SecurityContext: added withTrustedRoots named optional parameter constructor, which defaults to false.
• Added a timeout parameter to Socket.connect, RawSocket.connect, SecureSocket.connect and RawSecureSocket.connect. If a connection attempt takes longer than the duration specified in timeout, a SocketException will be thrown. Note: if the duration specified in timeout is greater than the OS level timeout, a timeout may occur sooner than specified in timeout.
• Stdin.hasTerminal added, which is true if stdin is attached to a terminal.
• WebSocket added static userAgent property.
• RandomAccessFile.close returns Future<void>
• Added IOOverrides.socketConnect.
• Added Dart-styled constants to ZLibOptions, FileMode, FileLock, FileSystemEntityType, FileSystemEvent, ProcessStartMode, ProcessSignal, InternetAddressType, InternetAddress, SocketDirection, SocketOption, RawSocketEvent, and StdioType, and deprecated the old SCREAMING_CAPS constants.
• Added the Dart-styled top-level constants zlib, gzip, and systemEncoding, and deprecated the old SCREAMING_CAPS top-level constants.
• Removed the top-level FileMode constants READ, WRITE, APPEND, WRITE_ONLY, and WRITE_ONLY_APPEND. Please use e.g. FileMode.read instead.
• Added X509Certificate.der, X509Certificate.pem, and X509Certificate.sha1.
• Added FileSystemEntity.fromRawPath constructor to allow for the creation of FileSystemEntity using Uint8List buffers.
• Dart-styled constants have been added for HttpStatus, HttpHeaders, ContentType, HttpClient, WebSocketStatus, CompressionOptions, and WebSocket. The SCREAMING_CAPS constants are marked deprecated. Note that HttpStatus.CONTINUE is now HttpStatus.continue_, and that e.g. HttpHeaders.FIELD_NAME is now HttpHeaders.fieldNameHeader.
• Deprecated Platform.packageRoot, which is only used for packages/ directory resolution which is no longer supported. It will now always return null, which is a value that was always possible for it to return previously.
• Adds HttpClient.connectionTimeout.
• Adds {Socket,RawSocket,SecureSocket}.startConnect. These return a ConnectionTask, which can be used to cancel an in-flight connection attempt.

dart:isolate

• Make Isolate.spawn take a type parameter representing the argument type of the provided function. This allows functions with arguments types other than Object in strong mode.
• Rename IMMEDIATE and BEFORE_NEXT_EVENT on Isolate to immediate and beforeNextEvent.
• Deprecated Isolate.packageRoot, which is only used for packages/ directory resolution which is no longer supported. It will now always return null, which is a value that was always possible for it to return previously.
• Deprecated packageRoot parameter in Isolate.spawnUri, which is was previously used only for packages/ directory resolution. That style of resolution is no longer supported in Dart 2.

<!-- Still need entries for all changes to dart:js since 1.x -->

dart.math

• Renamed E, LN10, LN, LOG2E, LOG10E, PI, SQRT1_2 and SQRT2 to e, ln10, ln, log2e, log10e, pi, sqrt1_2 and sqrt2.

dart.mirrors

• Added IsolateMirror.loadUri, which allows dynamically loading additional code.
• Marked MirrorsUsed as deprecated. The MirrorsUsed annotation was only used to inform the dart2js compiler about how mirrors were used, but dart2js no longer supports the mirrors library altogether.

<!-- Still need entries for all changes to dart:svg since 1.x -->

dart:typed_data

• Added Unmodifiable view classes over all List types.
• Renamed BYTES_PER_ELEMENT to bytesPerElement on all typed data lists.
• Renamed constants XXXX through WWWW on Float32x4 and Int32x4 to lower-case xxxx through wwww.
• Renamed Endinanness to Endian and its constants from BIG_ENDIAN, LITTLE_ENDIAN and HOST_ENDIAN to little, big and host.

<!-- Still need entries for all changes to dart:web_audio,web_gl,web_sql since 1.x -->

Dart VM

• Support for MIPS has been removed.

• Dart int is now restricted to 64 bits. On overflow, arithmetic operations wrap around, and integer literals larger than 64 bits are not allowed. See https://github.com/dart-lang/sdk/blob/main/docs/language/informal/int64.md for details.

• The Dart VM no longer attempts to perform packages/ directory resolution (for loading scripts, and in Isolate.resolveUri). Users relying on packages/ directories should switch to .packages files.

Dart for the Web

• Expose JavaScript Promise APIs using Dart futures. For example, BackgroundFetchManager.get is defined as:

    Future<BackgroundFetchRegistration> get(String id)
  

  It can be used like:

  BackgroundFetchRegistration result = await fetchMgr.get('abc');
  

  The underlying JS Promise-to-Future mechanism will be exposed as a public API in the future.

Dart Dev Compiler (DDC)

• dartdevc will no longer throw an error from is checks that return a different result in weak mode (SDK issue 28988). For example:

  main() {
    List l = [];
    // Prints "false", does not throw.
    print(l is List<String>);
  }
  

• Failed as casts on Iterable<T>, Map<T>, Future<T>, and Stream<T> are no longer ignored. These failures were ignored to make it easier to migrate Dart 1 code to strong mode, but ignoring them is a hole in the type system. This closes part of that hole. (We still need to stop ignoring "as" cast failures on function types, and implicit cast failures on the above types and function types.)

dart2js

• dart2js now compiles programs with Dart 2.0 semantics. Apps are expected to be bigger than before, because Dart 2.0 has many more implicit checks (similar to the --checked flag in Dart 1.0).

  We exposed a --omit-implicit-checks flag which removes most of the extra implicit checks. Only use this if you have enough test coverage to know that the app will work well without the checks. If a check would have failed and it is omitted, your app may crash or behave in unexpected ways. This flag is similar to --trust-type-annotations in Dart 1.0.

• dart2js replaced its front-end with the common front-end (CFE). Thanks to the CFE, dart2js errors are more consistent with all other Dart tools.

• dart2js replaced its source-map implementation. There aren't any big differences, but more data is emitted for synthetic code generated by the compiler.

• dart:mirrors support was removed. Frameworks are encouraged to use code-generation instead. Conditional imports indicate that mirrors are not supported, and any API in the mirrors library will throw at runtime.

• The generated output of dart2js can now be run as a webworker.

• dart:isolate support was removed. To launch background tasks, please use webworkers instead. APIs for webworkers can be accessed from dart:html or JS-interop.

• dart2js no longer supports the --package-root flag. This flag was deprecated in favor of --packages long ago.

Tool Changes

Analyzer

• The analyzer will no longer issue a warning when a generic type parameter is used as the type in an instance check. For example:

  test<T>() {
    print(3 is T); // No warning
  }
  

• New static checking of @visibleForTesting elements. Accessing a method, function, class, etc. annotated with @visibleForTesting from a file not in a test/ directory will result in a new hint (issue 28273).

• Static analysis now respects functions annotated with @alwaysThrows (issue 31384).

• New hints added:

  • NULL_AWARE_BEFORE_OPERATOR when an operator is used after a null-aware access. For example:

    x?.a - ''; // HINT
    

  • NULL_AWARE_IN_LOGICAL_OPERATOR when an expression with null-aware access is used as a condition in logical operators. For example:

    x.a || x?.b; // HINT
    

• The command line analyzer (dartanalyzer) and the analysis server no longer treat directories named packages specially. Previously they had ignored these directories - and their contents - from the point of view of analysis. Now they'll be treated just as regular directories. This special-casing of packages directories was to support using symlinks for package: resolution; that functionality is now handled by .packages files.

• New static checking of duplicate shown or hidden names in an export directive (issue 33182).

• The analysis server will now only analyze code in Dart 2 mode ('strong mode'). It will emit warnings for analysis options files that have strong-mode: false set (and will emit a hint for strong-mode: true, which is no longer necessary).

• The dartanalyzer --strong flag is now deprecated and ignored. The command-line analyzer now only analyzes code in strong mode.

dartfmt

• Support assert() in const constructor initializer lists.

• Better formatting for multi-line strings in argument lists.

• Force splitting an empty block as the then body of an if with an else.

• Support metadata annotations on enum cases.

• Add --fix to remove unneeded new and const keywords, and change : to = before named parameter default values.

• Change formatting rules around static methods to uniformly format code with and without new and const.

• Format expressions inside string interpolation.

Pub

• Pub has a brand new version solver! It supports all the same features as the old version solver, but it's much less likely to stall out on difficult package graphs, and it's much clearer about why a solution can't be found when version solving fails.

• Remove support for transformers, pub build, and pub serve. Use the [new build system][transformers] instead.

• There is now a default SDK constraint of <2.0.0 for any package with no existing upper bound. This allows us to move more safely to 2.0.0. All new packages published on pub will now require an upper bound SDK constraint so future major releases of Dart don't destabilize the package ecosystem.

  All SDK constraint exclusive upper bounds are now treated as though they allow pre-release versions of that upper bound. For example, the SDK constraint >=1.8.0 <2.0.0 now allows pre-release SDK versions such as 2.0.0-beta.3.0. This allows early adopters to try out packages that don't explicitly declare support for the new version yet. You can disable this functionality by setting the PUB_ALLOW_PRERELEASE_SDK environment variable to false.

• Allow depending on a package in a subdirectory of a Git repository. Git dependencies may now include a path parameter, indicating that the package exists in a subdirectory of the Git repository. For example:

  dependencies:
    foobar:
      git:
        url: git://github.com/dart-lang/multi_package_repo
        path: pkg/foobar
  

• Added an --executables option to pub deps command. This will list all available executables that can be run with pub run.

• The Flutter sdk source will now look for packages in flutter/bin/cache/pkg/ as well as flutter/packages/. In particular, this means that packages can depend on the sky_engine package from the sdk source (issue 1775).

• Pub now caches compiled packages and snapshots in the .dart_tool/pub directory, rather than the .pub directory (issue 1795).

• Other bug fixes and improvements.

• Documentation improvements.
• Deprecate use of DTDConnection in favor of DartToolingDaemon.

• Solidified interface with dart tooling daemon.
• Added FileSystem service interface.

• Added types to service and extension exports.

• Added service and extension for accessing the file system through DTD.

• Initial version.