meta

• One new TargetKind is introduced: TargetKind.importDirective, which indicates an annotation is valid on an import directive.

• Change private types in the public API signatures to Object.
• Update documentation to follow the "single line first paragraph" style.
• Make visibleForTesting documentation match actual behavior: The annotated member can be used in the test/ directory of other packages.

Patch release, resolves two issues and improves performance:

• Debugger: Fixes a bug that crashes the VM (SDK issue 26941)

• VM: Fixes an optimizer bug involving closures, try, and await (SDK issue 26948)

• Dart2js: Speeds up generated code on Firefox (https://codereview.chromium.org/2180533002)

Core library changes

• dart:core
  • Improved performance when parsing some common URIs.
  • Fixed bug in Uri.resolve (SDK issue 26804).
• dart:io
  • Adds file locking modes FileLock.BLOCKING_SHARED and FileLock.BLOCKING_EXCLUSIVE.

Core library changes

• dart:convert

  • Deprecate ChunkedConverter which was erroneously added in 1.16.

• dart:core

  • Uri.replace supports iterables as values for the query parameters.
  • Uri.parseIPv6Address returns a Uint8List.

• dart:io

  • Added NetworkInterface.listSupported, which is true when NetworkInterface.list is supported, and false otherwise. Currently, NetworkInterface.list is not supported on Android.

Tool Changes

• Pub

  • TAR files created while publishing a package on Mac OS and Linux now use a more portable format.

  • Errors caused by invalid arguments now print the full usage information for the command.

  • SDK constraints for dependency overrides are no longer considered when determining the total SDK constraint for a lockfile.

  • A bug has been fixed in which a lockfile was considered up-to-date when it actually wasn't.

  • A bug has been fixed in which pub get --offline would crash when a prerelease version was selected.

• Dartium and content shell

  • Debugging Dart code inside iframes improved, was broken.

Core library changes

• dart:convert

  • Added BASE64URL codec and corresponding Base64Codec.urlSafe constructor.

  • Introduce ChunkedConverter and deprecate chunked methods on Converter.

• dart:html

  There have been a number of BREAKING changes to align APIs with recent changes in Chrome. These include:

  • Chrome's ShadowRoot interface no longer has the methods getElementById, getElementsByClassName, and getElementsByTagName, e.g.,

    elem.shadowRoot.getElementsByClassName('clazz')
    

    should become:

    elem.shadowRoot.querySelectorAll('.clazz')
    

  • The clipboardData property has been removed from KeyEvent and Event. It has been moved to the new ClipboardEvent class, which is now used by copy, cut, and paste events.

  • The layer property has been removed from KeyEvent and UIEvent. It has been moved to MouseEvent.

  • The Point get page property has been removed from UIEvent. It still exists on MouseEvent and Touch.

  There have also been a number of other additions and removals to dart:html, dart:indexed_db, dart:svg, dart:web_audio, and dart:web_gl that correspond to changes to Chrome APIs between v39 and v45. Many of the breaking changes represent APIs that would have caused runtime exceptions when compiled to JavaScript and run on recent Chrome releases.

• dart:io

  • Added SecurityContext.alpnSupported, which is true if a platform supports ALPN, and false otherwise.

JavaScript interop

For performance reasons, a potentially BREAKING change was added for libraries that use JS interop. Any Dart file that uses @JS annotations on declarations (top-level functions, classes or class members) to interop with JavaScript code will require that the file have the annotation @JS() on a library directive.

@JS()
library my_library;

The analyzer will enforce this by generating the error:

The @JS() annotation can only be used if it is also declared on the library directive.

If part file uses the @JS() annotation, the library that uses the part should have the @JS() annotation e.g.,

// library_1.dart
@JS()
library library_1;

import 'package:js/js.dart';

part 'part_1.dart';

// part_1.dart
part of library_1;

@JS("frameworkStabilizers")
external List<FrameworkStabilizer> get frameworkStabilizers;

If your library already has a JS module e.g.,

@JS('array.utils')
library my_library;

Then your library will work without any additional changes.

Analyzer

• Static checking of for in statements. These will now produce static warnings:

  // Not Iterable.
  for (var i in 1234) { ... }
  
  // String cannot be assigned to int.
  for (int n in <String>["a", "b"]) { ... }
  

Tool Changes

• Pub

  • pub serve now provides caching headers that should improve the performance of requesting large files multiple times.

  • Both pub get and pub upgrade now have a --no-precompile flag that disables precompilation of executables and transformed dependencies.

  • pub publish now resolves symlinks when publishing from a Git repository. This matches the behavior it always had when publishing a package that wasn't in a Git repository.

• Dart Dev Compiler

  • The experimental dartdevc executable has been added to the SDK.

  • It will help early adopters validate the implementation and provide feedback. dartdevc is not yet ready for production usage.

  • Read more about the Dart Dev Compiler here.

Core library changes

• dart:async

  • Made StreamView class a const class.

• dart:core

  • Added Uri.queryParametersAll to handle multiple query parameters with the same name.

• dart:io

  • Added SecurityContext.usePrivateKeyBytes, SecurityContext.useCertificateChainBytes, SecurityContext.setTrustedCertificatesBytes, and SecurityContext.setClientAuthoritiesBytes.
  • Breaking The named directory argument of SecurityContext.setTrustedCertificates has been removed.
  • Added support to SecurityContext for PKCS12 certificate and key containers.
  • All calls in SecurityContext that accept certificate data now accept an optional named parameter password, similar to SecurityContext.usePrivateKeyBytes, for use as the password for PKCS12 data.

Tool changes

• Dartium and content shell

  • The Chrome-based tools that ship as part of the Dart SDK - Dartium and content shell - are now based on Chrome version 45 (instead of Chrome 39).
  • Dart browser libraries (dart:html, dart:svg, etc) have not been updated.
    • These are still based on Chrome 39.
    • These APIs will be updated in a future release.
  • Note that there are experimental APIs which have changed in the underlying browser, and will not work with the older libraries. For example, Element.animate.

• dartfmt - upgraded to v0.2.4

  • Better handling for long collections with comments.
  • Always put member metadata annotations on their own line.
  • Indent functions in named argument lists with non-functions.
  • Force the parameter list to split if a split occurs inside a function-typed parameter.
  • Don't force a split for before a single named argument if the argument itself splits.

Service protocol changes

• Fixed a documentation bug where the field extensionRPCs in Isolate was not marked optional.

Experimental language features

• Added support for configuration-specific imports. On the VM and dart2js, they can be enabled with --conditional-directives.

  The analyzer requires additional configuration:

  analyzer:
    language:
      enableConditionalDirectives: true
  

  Read about configuring the analyzer for more details.

Core library changes

• dart:async

  • Added Future.any static method.
  • Added Stream.fromFutures constructor.

• dart:convert

  • Base64Decoder.convert now takes optional start and end parameters.

• dart:core

  • Added current getter to StackTrace class.
  • Uri class added support for data URIs
    • Added two new constructors: dataFromBytes and dataFromString.
    • Added a data getter for data: URIs with a new UriData class for the return type.
  • Added growable parameter to List.filled constructor.
  • Added microsecond support to DateTime: DateTime.microsecond, DateTime.microsecondsSinceEpoch, and new DateTime.fromMicrosecondsSinceEpoch.

• dart:math

  • Random added a secure constructor returning a cryptographically secure random generator which reads from the entropy source provided by the embedder for every generated random value.

• dart:io

  • Platform added a static isIOS getter and Platform.operatingSystem may now return ios.
  • Platform added a static packageConfig getter.
  • Added support for WebSocket compression as standardized in RFC 7692.
  • Compression is enabled by default for all WebSocket connections.
    • The optionally named parameter compression on the methods WebSocket.connect, WebSocket.fromUpgradedSocket, and WebSocketTransformer.upgrade and the WebSocketTransformer constructor can be used to modify or disable compression using the new CompressionOptions class.

• dart:isolate

  • Added experimental support for Package Resolution Configuration.
    • Added packageConfig and packageRoot instance getters to Isolate.
    • Added a resolvePackageUri method to Isolate.
    • Added named arguments packageConfig and automaticPackageResolution to the Isolate.spawnUri constructor.

Tool changes

• dartfmt

  • Better line splitting in a variety of cases.

  • Other optimizations and bug fixes.

• Pub

  • Breaking: Pub now eagerly emits an error when a pubspec's "name" field is not a valid Dart identifier. Since packages with non-identifier names were never allowed to be published, and some of them already caused crashes when being written to a .packages file, this is unlikely to break many people in practice.

  • Breaking: Support for barback versions prior to 0.15.0 (released July

    1. has been dropped. Pub will no longer install these older barback versions.

  • pub serve now GZIPs the assets it serves to make load times more similar to real-world use-cases.

  • pub deps now supports a --no-dev flag, which causes it to emit the dependency tree as it would be if no dev_dependencies were in use. This makes it easier to see your package's dependency footprint as your users will experience it.

  • pub global run now detects when a global executable's SDK constraint is no longer met and errors out, rather than trying to run the executable anyway.

  • Pub commands that check whether the lockfile is up-to-date (pub run, pub deps, pub serve, and pub build) now do additional verification. They ensure that any path dependencies' pubspecs haven't been changed, and they ensure that the current SDK version is compatible with all dependencies.

  • Fixed a crashing bug when using pub global run on a global script that didn't exist.

  • Fixed a crashing bug when a pubspec contains a dependency without a source declared.

Language changes

• Null-aware operators
  • ??: if null operator. expr1 ?? expr2 evaluates to expr1 if not null, otherwise expr2.
  • ??=: null-aware assignment. v ??= expr causes v to be assigned expr only if v is null.
  • x?.p: null-aware access. x?.p evaluates to x.p if x is not null, otherwise evaluates to null.
  • x?.m(): null-aware method invocation. x?.m() invokes m only if x is not null.

Core library changes

• dart:async

  • StreamController added setters for the onListen, onPause, onResume and onCancel callbacks.

• dart:convert

  • LineSplitter added a split static method returning an Iterable.

• dart:core

  • Uri class now perform path normalization when a URI is created. This removes most .. and . sequences from the URI path. Purely relative paths (no scheme or authority) are allowed to retain some leading "dot" segments. Also added hasAbsolutePath, hasEmptyPath, and hasScheme properties.

• dart:developer

  • New log function to transmit logging events to Observatory.

• dart:html

  • NodeTreeSanitizer added the const trusted field. It can be used instead of defining a NullTreeSanitizer class when calling setInnerHtml or other methods that create DOM from text. It is also more efficient, skipping the creation of a DocumentFragment.

• dart:io

  • Added two new file modes, WRITE_ONLY and WRITE_ONLY_APPEND for opening a file write only. eaeecf2
  • Change stdout/stderr to binary mode on Windows. 4205b29

• dart:isolate

  • Added onError, onExit and errorsAreFatal parameters to Isolate.spawnUri.

• dart:mirrors

  • InstanceMirror.delegate moved up to ObjectMirror.
  • Fix InstanceMirror.getField optimization when the selector is an operator.
  • Fix reflective NoSuchMethodErrors to match their non-reflective counterparts when due to argument mismatches. (VM only)

Tool changes

• Documentation tools

  • dartdoc is now the default tool to generate static HTML for API docs. Learn more.

  • docgen and dartdocgen have been deprecated. Currently plan is to remove them in 1.13.

• Formatter (dartfmt)

  • Over 50 bugs fixed.

  • Optimized line splitter is much faster and produces better output on complex code.

• Observatory

  • Allocation profiling.

  • New feature to display output from logging.

  • Heap snapshot analysis works for 64-bit VMs.

  • Improved ability to inspect typed data, regex and compiled code.

  • Ability to break on all or uncaught exceptions from Observatory's debugger.

  • Ability to set closure-specific breakpoints.

  • 'anext' - step past await/yield.

  • Preserve when a variable has been expanded/unexpanded in the debugger.

  • Keep focus on debugger input box whenever possible.

  • Echo stdout/stderr in the Observatory debugger. Standalone-only so far.

  • Minor fixes to service protocol documentation.

• Pub

  • Breaking: various commands that previously ran pub get implicitly no longer do so. Instead, they merely check to make sure the ".packages" file is newer than the pubspec and the lock file, and fail if it's not.

  • Added support for --verbosity=error and --verbosity=warning.

  • pub serve now collapses multiple GET requests into a single line of output. For full output, use --verbose.

  • pub deps has improved formatting for circular dependencies on the entrypoint package.

  • pub run and pub global run

    • Breaking: to match the behavior of the Dart VM, executables no longer run in checked mode by default. A --checked flag has been added to run them in checked mode manually.

    • Faster start time for executables that don't import transformed code.

    • Binstubs for globally-activated executables are now written in the system encoding, rather than always in UTF-8. To update existing executables, run pub cache repair.

  • pub get and pub upgrade

    • Pub will now generate a ".packages" file in addition to the "packages" directory when running pub get or similar operations, per the package spec proposal. Pub now has a --no-package-symlinks flag that will stop "packages" directories from being generated at all.

    • An issue where HTTP requests were sometimes made even though --offline was passed has been fixed.

    • A bug with --offline that caused an unhelpful error message has been fixed.

    • Pub will no longer time out when a package takes a long time to download.

  • pub publish

    • Pub will emit a non-zero exit code when it finds a violation while publishing.

    • .gitignore files will be respected even if the package isn't at the top level of the Git repository.

  • Barback integration

    • A crashing bug involving transformers that only apply to non-public code has been fixed.

    • A deadlock caused by declaring transformer followed by a lazy transformer (such as the built-in $dart2js transformer) has been fixed.

    • A stack overflow caused by a transformer being run multiple times on the package that defines it has been fixed.

    • A transformer that tries to read a nonexistent asset in another package will now be re-run if that asset is later created.

VM Service Protocol Changes

• BREAKING The service protocol now sends JSON-RPC 2.0-compatible server-to-client events. To reflect this, the service protocol version is now 2.0.

• The service protocol now includes a "jsonrpc" property in its responses, as opposed to "json-rpc".

• The service protocol now properly handles requests with non-string ids. Numeric ids are no longer converted to strings, and null ids now don't produce a response.

• Some RPCs that didn't include a "jsonrpc" property in their responses now include one.

Core library changes

• dart:core

  • Iterable added an empty constructor. dcf0286
  • Iterable can now be extended directly. An alternative to extending IterableBase from dart:collection.
  • List added an unmodifiable constructor. r45334
  • Map added an unmodifiable constructor. r45733
  • int added a gcd method. a192ef4
  • int added a modInverse method. f6f338c
  • StackTrace added a fromString constructor. 68dd6f6
  • Uri added a directory constructor. d8dbb4a
  • List iterators may not throw ConcurrentModificationError as eagerly in release mode. In checked mode, the modification check is still as eager as possible. r45198

• dart:developer - NEW

  • Replaces the deprecated dart:profiler library.
  • Adds new functions debugger and inspect. 6e42aec

• dart:io

  • FileSystemEntity added a uri property. 8cf32dc
  • Platform added a static resolvedExecutable property. c05c8c6

• dart:html

  • Element methods, appendHtml and insertAdjacentHtml now take nodeValidator and treeSanitizer parameters, and the inputs are consistently sanitized. r45818 announcement

• dart:isolate

  • BREAKING The positional priority parameter of Isolate.ping and Isolate.kill is now a named parameter named priority.
  • BREAKING Removed the Isolate.AS_EVENT priority.
  • Isolate methods ping and addOnExitListener now have a named parameter response. r45092
  • Isolate.spawnUri added a named argument checked.
  • Remove the experimental state of the API.

• dart:profiler - DEPRECATED

  • This library will be removed in 1.12. Use dart:developer instead.

Tool changes

• This is the first release that does not include the Eclipse-based Dart Editor. See dart.dev/tools for alternatives.
• This is the last release that ships the (unsupported) dart2dart (aka dart2js --output-type=dart) utility as part of dart2js

Core library changes

• dart:convert

  • POTENTIALLY BREAKING Fix behavior of HtmlEscape. It no longer escapes no-break space (U+00A0) anywhere or forward slash (/, U+002F) in element context. Slash is still escaped using HtmlEscapeMode.UNKNOWN. r45003, r45153, r45189

• dart:core

  • Uri.parse added start and end positional arguments.

• dart:html

  • POTENTIALLY BREAKING CssClassSet method arguments must now be 'tokens', i.e. non-empty strings with no white-space characters. The implementation was incorrect for class names containing spaces. The fix is to forbid spaces and provide a faster implementation. Announcement

• dart:io

  • ProcessResult now exposes a constructor.
  • import and Isolate.spawnUri now supports the Data URI scheme on the VM.

Tool Changes

pub

• Running pub run foo within a package now runs the foo executable defined by the foo package. The previous behavior ran bin/foo. This makes it easy to run binaries in dependencies, for instance pub run test.

• On Mac and Linux, signals sent to pub run and forwarded to the child command.

Language changes

• Support for async, await, sync*, async*, yield, yield*, and await for. See the the language tour for more details.

• Enum support is fully enabled. See the language tour for more details.

Tool changes

• The formatter is much more comprehensive and generates much more readable code. See its tool page for more details.

• The analysis server is integrated into the IntelliJ plugin and the Dart editor. This allows analysis to run out-of-process, so that interaction remains smooth even for large projects.

• Analysis supports more and better hints, including unused variables and unused private members.

Core library changes

Highlights

• There's a new model for shared server sockets with no need for a Socket reference.

• A new, much faster regular expression engine.

• The Isolate API now works across the VM and dart2js.

Details

For more information on any of these changes, see the corresponding documentation on the Dart API site.

• dart:async:

  • Future.wait added a new named argument, cleanUp, which is a callback that releases resources allocated by a successful Future.

  • The SynchronousStreamController class was added as an explicit name for the type returned when the sync argument is passed to new StreamController.

• dart:collection: The new SplayTreeSet.from(Iterable) constructor was added.

• dart:convert: Utf8Encoder.convert and Utf8Decoder.convert added optional start and end arguments.

• dart:core:

  • RangeError added new static helper functions: checkNotNegative, checkValidIndex, checkValidRange, and checkValueInInterval.

  • int added the modPow function.

  • String added the replaceFirstMapped and replaceRange functions.

• dart:io:

  • Support for locking files to prevent concurrent modification was added. This includes the File.lock, File.lockSync, File.unlock, and File.unlockSync functions as well as the FileLock class.

  • Support for starting detached processes by passing the named mode argument (a ProcessStartMode) to Process.start. A process can be fully attached, fully detached, or detached except for its standard IO streams.

  • HttpServer.bind and HttpServer.bindSecure added the v6Only named argument. If this is true, only IPv6 connections will be accepted.

  • HttpServer.bind, HttpServer.bindSecure, ServerSocket.bind, RawServerSocket.bind, SecureServerSocket.bind and RawSecureServerSocket.bind added the shared named argument. If this is true, multiple servers or sockets in the same Dart process may bind to the same address, and incoming requests will automatically be distributed between them.

  • Deprecation: the experimental ServerSocketReference and RawServerSocketReference classes, as well as getters that returned them, are marked as deprecated. The shared named argument should be used instead. These will be removed in Dart 1.10.

  • Socket.connect and RawSocket.connect added the sourceAddress named argument, which specifies the local address to bind when making a connection.

  • The static Process.killPid method was added to kill a process with a given PID.

  • Stdout added the nonBlocking instance property, which returns a non-blocking IOSink that writes to standard output.

• dart:isolate:

  • The static getter Isolate.current was added.

  • The Isolate methods addOnExitListener, removeOnExitListener, setErrorsFatal, addOnErrorListener, and removeOnErrorListener now work on the VM.

  • Isolates spawned via Isolate.spawn now allow most objects, including top-level and static functions, to be sent between them.

• Introduce @reopen to annotate class or mixin declarations that can safely extend classes marked base, final or interface.
• Introduce @MustBeOverridden to annotate class or mixin members which must be overridden in all subclasses.
• Deprecate @alwaysThrows, which can be replaced by using a return type of 'Never'.

• dart:collection: SplayTree added the toSet function.

• dart:convert: The JsonUtf8Encoder class was added.

• dart:core:

  • The IndexError class was added for errors caused by an index being outside its expected range.

  • The new RangeError.index constructor was added. It forwards to new IndexError.

  • RangeError added three new properties. invalidProperty is the value that caused the error, and start and end are the minimum and maximum values that the value is allowed to assume.

  • new RangeError.value and new RangeError.range added an optional message argument.

  • The new String.fromCharCodes constructor added optional start and end arguments.

• dart:io:

  • Support was added for the Application-Layer Protocol Negotiation extension to the TLS protocol for both the client and server.

  • SecureSocket.connect, SecureServerSocket.bind, RawSecureSocket.connect, RawSecureSocket.secure, RawSecureSocket.secureServer, and RawSecureServerSocket.bind added a supportedProtocols named argument for protocol negotiation.

  • RawSecureServerSocket added a supportedProtocols field.

  • RawSecureSocket and SecureSocket added a selectedProtocol field which contains the protocol selected during protocol negotiation.

Tool changes

• pub now generates binstubs for packages that are globally activated so that they can be put on the user's PATH and used as normal executables. See the pub global activate documentation.

• When using dart2js, deferred loading now works with multiple Dart apps on the same page.

Core library changes

• dart:async: Zone, ZoneDelegate, and ZoneSpecification added the errorCallback function, which allows errors that have been programmatically added to a Future or Stream to be intercepted.

• dart:io:

  • Breaking change: HttpClient.close must be called for all clients or they will keep the Dart process alive until they time out. This fixes the handling of persistent connections. Previously, the client would shut down immediately after a request.

  • Breaking change: HttpServer no longer compresses all traffic by default. The new autoCompress property can be set to true to re-enable compression.

• dart:isolate: Isolate.spawnUri added the optional packageRoot argument, which controls how it resolves package: URIs.

• Remove TargetKindExtension. Adding it was a breaking change, because there are clients, e.g. analyze 1.7.0, that also declare an extension on TargetKind, and also declare get displayString. This causes a conflict.

• Add TargetKindExtension.displayString.

• Introduce TargetKind.topLevelVariable that indicates that an annotation is valid on any top-level variable declaration.
• Introduce @useResult to annotate methods, fields, or getters that return values that should be used - stored, passed as arguments, etc.
• Updates for documentation.

• Stable release for null safety.

• Update SDK constraints to >=2.12.0-0 <3.0.0 based on beta release guidelines.

• Allow prerelease versions of the 2.12 SDK.

• Introduce @internal to annotate elements that should not be used outside of the package in which the element is declared.

• Allow 2.10 stable and 2.11.0 dev SDK versions.

• Update for the 2.10 dev SDK.

• Allow the <=2.9.10 stable SDK.

• Opt into null safety.

• Removed unawaited because the attempt to move it from package:pedantic caused too many issues. If you see errors about unawaited being declared in two places, please update the version constraints for meta to 1.2.2 or later.

• Fixed a bug by adding an import of dart:async so that the code really is compatible with the lower bound of the SDK constraints.

• Introduce unawaited to mark invocations that return a Future where it's intentional that the future is not being awaited. (Moved from package:pedantic.)
• Introduce @doNotStore to annotate methods, getters and functions to indicate that values obtained by invoking them should not be stored in a field or top-level variable.

• Introduce @nonVirtual to annotate instance members that should not be overridden in subclasses or when mixed in.

• Introduce @sealed to declare that a class or mixin is not allowed as a super-type.

  Only classes in the same package as a class or mixin annotated with @sealed may extend, implement or mix-in the annotated class or mixin. (SDK issue 27372).

• Set max SDK version to <3.0.0.

• Introduce @isTest and @isTestGroup to declare a function that is a test, or a test group.

• Rollback SDK constraint update for 2.0.0. No longer needed.

• Update SDK constraint to be 2.0.0 dev friendly.

• Introduce @alwaysThrows to declare that a function always throws (SDK issue 17999). This is first available in Dart SDK 1.25.0-dev.1.0.

  import 'package:meta/meta.dart';
  
  // Without knowing that [failBigTime] always throws, it looks like this
  // function might return without returning a bool.
  bool fn(expected, actual) {
    if (expected != actual)
      failBigTime(expected, actual);
    else
      return True;
  }
  
  @alwaysThrows
  void failBigTime(expected, actual) {
    throw new StateError('Expected $expected, but was $actual.');
  }
  

• Introduce @experimental to annotate a library, or any declaration that is part of the public interface of a library (such as top-level members, class members, and function parameters) to indicate that the annotated API is experimental and may be removed or changed at any-time without updating the version of the containing package, despite the fact that it would otherwise be a breaking change.

• Introduce @virtual to allow field overrides in strong mode (SDK issue 27384).

  import 'package:meta/meta.dart' show virtual;
  class Base {
    @virtual int x;
  }
  class Derived extends Base {
    int x;
  
    // Expose the hidden storage slot:
    int get superX => super.x;
    set superX(int v) { super.x = v; }
  }
  

• Introduce @checked to override a method and tighten a parameter type (SDK issue 25578).

  import 'package:meta/meta.dart' show checked;
  class View {
    addChild(View v) {}
  }
  class MyView extends View {
    // this override is legal, it will check at runtime if we actually
    // got a MyView.
    addChild(@checked MyView v) {}
  }
  main() {
    dynamic mv = new MyView();
    mv.addChild(new View()); // runtime error
  }
  

• Introduce @visibleForTesting annotation for declarations that may be referenced only in the library or in a test.

• Updated @factory to allow statics and methods returning null.

• Fixed markdown in dartdocs.

• Introduce @optionalTypeArgs annotation for classes whose type arguments are to be treated as optional.

• Added new Required constructor with a means to specify a reason to explain why a parameter is required.

• Introduce @factory annotation for methods that must either be abstract or must return a newly allocated object.
• Introduce @literal annotation that indicates that any invocation of a constructor must use the keyword const unless one or more of the arguments to the constructor is not a compile-time constant.

• Introduce @protected annotation for members that must only be called from instance members of subclasses.
• Introduce @required annotation for optional parameters that should be treated as required.
• Introduce @mustCallSuper annotation for methods that must be invoked by all overriding methods.