chore(deps): update dependency dart to v3 #66
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This PR contains the following updates:
>=2.7.0 <3.0.0
-><4.0.0
Release Notes
dart-lang/sdk (dart)
v3.7.0
Compare Source
Released on: 2025-02-12
Language
Dart 3.7 adds wildcard variables to the language. To use them, set your
package's [SDK constraint][language version] lower bound to 3.7 or greater
(
sdk: '^3.7.0'
).Wildcard Variables
Local variables and parameters named
_
are now non-binding and they canbe declared multiple times without collisions. You will no longer be able to use
these variables nor access their values. All wildcard variable declaration types
that have this behavior are described in the
wildcard variables specification.
Top-level variables, top-level function names, type names, member names, etc.
are unchanged. They can be named
_
and used as they are today.These are a few examples of where wildcard variables can be used:
Other Language Changes
Null
using
is
oras
, this type promotion is now properly accounted for inreachability analysis. This makes the type system more self-consistent,
because it mirrors the behavior of promoted local variables. This change is
not expected to make any difference in practice.
Tools
Analyzer
declaration.
prefer_relative_imports
andalways_use_package_imports
lint rules.~/
operation into/
, when the~/
operation is not available.
await
if the expression is currentlynot assignable, but awaiting it would make it assignable.
forEach
call into a for-loop nowconsider the
prefer_final_in_for_each
andalways_specify_types
lintrules.
cascade_invocations
lint rule violation.Expanded
widget,and with a
Flexible
widget.else-block to read
else if
.use_decorated_box
by swapping theContainer
withColoredBox
as suggested by the lint.the
show
combinator on an existing import.import directive with the given prefix.
hide
combinator.
show
combinator, and optionally a prefix.initializer of a late field.
prefer_const_declarations
lint rule, preferring to addconst
to a variabledeclaration rather than the initial value.
on
keyword in an extension declaration.override.
(Thanks @FMorschel for the above enhancements!
sort_constructors_first
lintrule.
function-typed parameters.
strict_top_level_inference
][strict_top_level_inference] lint rule.unnecessary_underscores
][unnecessary_underscores] lint rule.specify_nonobvious_property_types
][specify_nonobvious_property_types] lint rule.omit_obvious_property_types
][omit_obvious_property_types] lint rule.unnecessary_async
][unnecessary_async] lint rule.unsafe_variance
][unsafe_variance] lint rule.package_api_docs
][package_api_docs] lint rule.unsafe_html
][unsafe_html] lint rule.Dart format
The formatter implements a new style better suited for the kind of
declarative code that many Dart users are writing today. The new style looks
similar to the style you get when you add trailing commas to argument lists,
except that now the formatter will add and remove those commas for you.
The
dart format
command uses the language version ofeach input file to determine which style it gets. If the language version is 3.6
or lower, the code is formatted with the old style. If 3.7 or later, it gets the
new tall style.
You typically control the language version by setting a min SDK constraint in
your package's pubspec. This means that when you update the SDK
constraint in your pubspec to move to 3.7, you are also opting in to the new
style.
In order to correctly determine the language version of each file it formats,
dart format
(like otherdart
commands) looks for apackage_config.json
file surrounding the files being formatted. This means that you need to run
dart pub get
before formatting code in your package. If you have formatchecks in your continuous integration server, you'll want to make sure it runs
dart pub get
too.We don't intend to support both styles indefinitely. At some point in the
future when most of the ecosystem is on 3.7 or later, support for the old style
will be removed.
In addition to the new formatting style, a number of other changes are included,
some of them breaking:
Project-wide page width configuration. By long request, you can now
configure your preferred formatting page width on a project-wide basis. When
formatting a file, the formatter will look in the file's directory and any
surrounding directories for an
analysis_options.yaml
file. If it finds one,it looks for YAML like so:
If it finds a page width matching that schema, then the file is formatted
using that width. Since the formatter will walk the surrounding directories
until it finds an
analysis_options.yaml
file, this can be used to globallyset the page width for an entire directory, package, or even collection of
packages. Since
analysis_options.yaml
files already support aninclude
key to reference other
analysis_options.yaml
files, you can define a singleconfiguration and share it across a number of packages.
Opting out a region of code from formatting. In code formatted using the
new style, you can use a pair of special marker comments to opt a region of
code out of automated formatting:
The comments must be exactly
// dart format off
and// dart format on
.A file may have multiple regions, but they can't overlap or nest.
This can be useful for highly structured data where custom layout helps the
reader understand the data, like large lists of numbers.
Overriding the page width for a single file. In code formatted
using the new tall style, you can use a special marker comment to control the
page width that it's formatted using:
This comment must appear before any code in the file and must match that
format exactly. The width set by the comment overrides the width set by any
surrounding
analysis_options.yaml
file.This feature is mainly for code generators that generate and immediately
format code but don't know about any surrounding
analysis_options.yaml
that might be configuring the page width. By inserting this comment in the
generated code before formatting, it ensures that the code generator's
behavior matches the behavior of
dart format
.End users should mostly use
analysis_options.yaml
for configuring theirpreferred page width (or do nothing and continue to use the default page width
of 80).
Breaking change: Remove support for
dart format --fix
. Instead, usedart fix
. It supports all of the fixes thatdart format --fix
could applyand many more.
Treat the
--stdin-name
name as a path when inferring language version.When reading input on stdin, the formatter still needs to know its language
version to know what style to apply. If the
--stdin-name
option is set, thenthat is treated as a file path and the formatter looks for a package config
surrounding that file path to infer the language version from.
If you don't want that behavior, pass in an explicit language version using
--language-version=
, or use--language-version=latest
to parse the inputusing the latest language version supported by the formatter.
If
--stdin-name
and--language-version
are both omitted, then theformatter parses stdin using the latest supported language version.
Rename the
--line-length
option to--page-width
. This is consistentwith the public API, internal implementation, and docs, which all use "page
width" to refer to the limit that the formatter tries to fit code into.
The
--line-length
name is still supported for backwards compatibility, butmay be removed at some point in the future. You're encouraged to move to
--page-width
. Use of this option (however it's named) is rare, and willlikely be even rarer now that project-wide configuration is supported, so
this shouldn't affect many users.
Dart to Javascript Compiler (dart2js)
The dart2js compiler which is invoked when the command 'dart compile js' is
used has been switched to use an AOT snapshot instead of a JIT snapshot.
Dart Development Compiler (dartdevc)
The dartdevc compiler and kernel_worker utility have been switched to use an
AOT snapshot instead of a JIT snapshot, the SDK build still includes a JIT
snapshot of these tools as package build/build_web_compiler depends on it. The
AOT snapshot can be used as follows to run DDC /bin/dartaotruntime /bin/snapshots/dartdevc_aot.dart.snapshot
Libraries
dart:html
dart:html
is marked deprecated and will be removed in an upcoming release.Users should migrate to using
dart:js_interop
andpackage:web
. See#59716.
dart:indexed_db
dart:indexed_db
is marked deprecated and will be removed in an upcomingrelease. Users should migrate to using
dart:js_interop
andpackage:web
.See #59716.
dart:io
HttpException
will be thrown byHttpClient
andHttpServer
if aNUL
(
0x00
) appears in a received HTTP header value.dart:svg
dart:svg
is marked deprecated and will be removed in an upcoming release.Users should migrate to using
dart:js_interop
andpackage:web
. See#59716.
dart:web_audio
dart:web_audio
is marked deprecated and will be removed in an upcomingrelease. Users should migrate to using
dart:js_interop
andpackage:web
.See #59716.
dart:web_gl
dart:web_gl
is marked deprecated and will be removed in an upcoming release.Users should migrate to using
dart:js_interop
andpackage:web
. See#59716.
dart:js
dart:js
is marked deprecated and will be removed in an upcoming release.Users should migrate to using
dart:js_interop
. See #59716.dart:js_util
dart:js_util
is marked deprecated and will be removed in an upcomingrelease. Users should migrate to using
dart:js_interop
. See #59716.v3.6.2
Compare Source
Released on: 2025-01-30
HttpServer
responses were not correctly encodedif a "Content-Type" header was set (issue #59719).
dart format
to parse code at language version 3.6 so that digitseparators can be parsed correctly (issue #59815, dart_style issue
#1630).
between new and legacy inspector events (issue #59884).
dart fix
on a folder that contains a library with multiplefiles and more than one needs a fix, the fix will now be applied correctly
only once to each file (issue #59572).
v3.6.1
Compare Source
Released on: 2025-01-08
pub get
will now delete stray.dart_tool/package_config.json
files in directories between theworkspace root and workspace directories. Preventing confusing behavior
when migrating a repository to pub workspaces (issue pub#4445).
the incorrect generic covariant field in a constant object (issue
#57084).
(issue #56552).
v3.6.0
Compare Source
Released on: 2024-12-11
Language
Dart 3.6 adds digit separators to the language. To use them, set your
package's [SDK constraint][language version] lower bound to 3.6 or greater
(
sdk: '^3.6.0'
).Digit separators
Digits in number literals (decimal integer literals, double literals,
scientific notation literals, and hexadecimal literals) can now include
underscores between digits, as "digit separators." The separators do not change
the value of a literal, but can serve to make the number more readable.
Separators are not allowed at the start of a number (this would be parsed as an
identifier), at the end of a number, or adjacent to another character in a
number, like
.
,x
, or thee
in scientific notation.to perform type inference on the operand of a
throw
expression has beenchanged from the "unknown type" to
Object
. This makes the type system moreself-consistent, because it reflects the fact that it's not legal to throw
null
. This change is not expected to make any difference in practice.Libraries
dart:io
Breaking Change #52444: Removed the
Platform()
constructor, whichhas been deprecated since Dart 3.1.
Breaking Change #53618:
HttpClient
now responds to a redirectthat is missing a "Location" header by throwing
RedirectException
, insteadof
StateError
.dart:js_interop
JSArrayBuffer
,JSDataView
, and concrete typed arraytypes e.g.
JSInt8Array
.length
and[]
/[]=
operators toJSArray
.toJSCaptureThis
sothis
is passed in from JavaScript to thecallback as the first parameter.
from
method onJSArray
to create aJSArray
from a givenJavaScript iterable or array-like object.
Tools
CFE
DOWN algorithms in the CFE are changed to match the specification
and the corresponding implementations in the Analyzer. The upper and
lower closures of type schemas are now computed just before they are
passed into the subtype testing procedure instead of at the very
beginning of the UP and DOWN algorithms.
Dart format
this.
orsuper.
.as
andif
clauses.Wasm compiler (dart2wasm)
dart.library.js
is now false on conditional imports indart2wasm. Note that it was already a static error to import
dart:js
directly (see #55266).
Pub
Support for workspaces. This allows you to develop and resolve multiple
packages from the same repo together. See https://dart.dev/go/pub-workspaces
for more info.
New command
dart pub bump
. Increments the version number of the currentpackage.
For example:
dart pub bump minor
will change the version from1.2.3
to1.3.0
.New validation:
dart pub publish
will warn if yourgit status
is notclean.
New flag
dart pub upgrade --unlock-transitive
.dart pub upgrade --unlock-transitive pkg
, will unlock and upgrade all thedependencies of
pkg
instead of justpkg
.Analyzer
use_truncating_division
][use_truncating_division] lint rule.omit_obvious_local_variable_types
][omit_obvious_local_variable_types] lint rule.specify_nonobvious_local_variable_types
][specify_nonobvious_local_variable_types] lint rule.avoid_futureor_void
][avoid_futureor_void] lint rule."invert conditional expression".
v3.5.4
Compare Source
v3.5.3
Compare Source
issue resulting in a missing tab bar when DevTools is embedded in
IntelliJ and Android Studio (issue#56607).
DevTools is opened instead of only the first time (issue#56607).
embedded in IntelliJ and Android Studio (issue#56607).
v3.5.2
Compare Source
ZLibDecoder
would incorrectly attempt to decompress datapast the end of the zlib footer (issue #56481).
dart
fromPATH
could result in some commands notworking as expected (issues #56080, #56306, #56499).
setContextRoots
requests orbeing provided incorrect context roots in multi-package workspaces (issue
#56475).
v3.5.1
Compare Source
include:
inanalysis_options.yaml
file in a nestedfolder in the workspace (issue#56464).
dart compile wasm
when optimizations areenabled (issue #56423).
dart2wasm
compiler in unsound-O3
/-O4
modes where aimplicit setter for a field of generic type will store
null
instead of thefield value (issue #56374).
dart2wasm
compiler that can trigger in certain situationswhen using partial instantiations of generic tear-offs (constructors or static
methods) in constant expressions (issue #56440).
also known is UP, is provided the missing implementation for
StructuralParameterType
objects. In some corner cases cases thelacking implementation resulted in a crash of the compiler (issue #56457).
v3.5.0
Compare Source
Language
Breaking Change #55418: The context used by the compiler to perform
type inference on the operand of an
await
expression has been changed tomatch the behavior of the analyzer. This change is not expected to make any
difference in practice.
Breaking Change #55436: The context used by the compiler to perform
type inference on the right hand side of an "if-null" expression (
e1 ?? e2
)has been changed to match the behavior of the analyzer. change is expected to
have low impact on real-world code. But in principle it could cause
compile-time errors or changes in runtime behavior by changing inferred
types. The old behavior can be restored by supplying explicit types.
Libraries
dart:core
DateTime
on the web platform now storesmicroseconds. The web implementation is now practically compatible with the
native implementation, where it is possible to round-trip a timestamp in
microseconds through a
DateTime
value without rounding the lowerdigits. This change might be breaking for apps that rely in some way on the
.microsecond
component always being zero, for example, expecting only threefractional second digits in the
toString()
representation. Smalldiscrepancies in arithmetic due to rounding of web integers may still occur
for extreme values, (1)
microsecondsSinceEpoch
outside the safe range,corresponding to dates with a year outside of 1685..2255, and (2) arithmetic
(
add
,subtract
,difference
) where theDuration
argument or resultexceeds 570 years.
dart:io
Breaking Change #55786:
SecurityContext
is nowfinal
. This meansthat
SecurityContext
can no longer be subclassed.SecurityContext
subclasses were never able to interoperate with other parts of
dart:io
.A
ConnectionTask
can now be created using an existingFuture<Socket>
.Fixes #55562.
dart:typed_data
Breaking Change #53785: The unmodifiable view classes for typed data
have been removed. These classes were deprecated in Dart 3.4.
To create an unmodifiable view of a typed-data object, use the
asUnmodifiableView()
methods added in Dart 3.3.Added superinterface
TypedDataList
to typed data lists, implementing bothList
andTypedData
. Allows abstracting over all such lists without losingaccess to either the
List
or theTypedData
members.A
ByteData
is still only aTypedData
, not a list.dart:js_interop
Breaking Change #55508:
importModule
now accepts aJSAny
insteadof a
String
to support other JS values as well, likeTrustedScriptURL
s.Breaking Change #55267:
isTruthy
andnot
now returnJSBoolean
instead of
bool
to be consistent with the other operators.Breaking Change
ExternalDartReference
no longer implementsObject
.ExternalDartReference
now accepts a type parameterT
with a bound ofObject?
to capture the type of the Dart object that is externalized.ExternalDartReferenceToObject.toDartObject
now returns aT
.ExternalDartReferenceToObject
andObjectToExternalDartReference
are nowextensions on
T
andExternalDartReference<T>
, respectively, whereT extends Object?
. See #55342 and #55536 for more details.Fixed some consistency issues with
Function.toJS
across all compilers.Specifically, calling
Function.toJS
on the same function gives you a new JSfunction (see issue #55515), the maximum number of arguments that are
passed to the JS function is determined by the static type of the Dart
function, and extra arguments are dropped when passed to the JS function in
all compilers (see #48186).
Tools
Analyzer
unintended_html_in_doc_comment
][unintended_html_in_doc_comment] lint rule.invalid_runtime_check_with_js_interop_types
][invalid_runtime_check_with_js_interop_types] lint rule.document_ignores
][document_ignores] lint rule.the switch becomes exhaustive.
const
keywords to child nodes, whereappropriate.
Pub
dart pub downgrade --tighten
to restrict lower bounds ofdependencies' constraints to the minimum that can be resolved.
Dart Runtime
The Dart VM only executes sound null safe code, running of unsound null
safe code using the option
--no-sound-null-safety
has been removed.Dart_NewListOf
andDart_IsLegacyType
functions areremoved from Dart C API.
Dart_DefaultCanonicalizeUrl
is removed from the Dart C API.v3.4.4
Compare Source
This is a patch release that:
Fixes an issue where pub would crash when failing to fetch advisories from
the server. (issue pub#4269).
Fixes an issue where
const bool.fromEnvironment('dart.library.ffi')
is trueand conditional import condition
dart.library.ffi
is true in dart2wasm.(issue #55948).
Fixes an issue where FFI calls with variadic arguments on MacOS Arm64
would mangle the arguments. (issue #55943).
v3.4.3
Compare Source
This is a patch release that:
Fixes an issue where
DART_VM_OPTIONS
were not correctly parsed forstandalone Dart executables created with
dart compile exe
(issue#55818).
Fixes a bug in dart2wasm that can result in a runtime error that says
array.new_fixed()
has a constant larger than 10000 (issue #55873).Adds support for
--enable-experiment
flag todart compile
wasm(issue #55894).
Fixes an issue in dart2wasm compiler that can result in incorrect
nullability of type parameter (see #55895).
Disallows
dart:ffi
imports in user code in dart2wasm (e.g. issue[#53910]) as dart2wasm's currently only supports a small subset of
dart:ffi
(issue #55890).v3.4.2
Compare Source
This is a patch release that:
Marks
dart compile wasm
as no longer experimental.Fixes two bugs in exception handling in
async
functions in dart2wasm(issues #55347, #55457).
Fixes restoration of
this
variable insync*
andasync
functions indart2wasm.
Implements missing control flow constructs (exceptions, switch/case with
yields) in
sync*
in dart2wasm (issues #51342, #51343).Fixes a bug dart2wasm compiler that surfaces as a compiler crash when indexing
lists where the compiler proofs the list to be constant and the index is
out-of-bounds (issue #55817).
v3.4.1
Compare Source
This is a patch release that:
Fixes a bug in the CFE which could manifest as compilation errors of Flutter
web apps when compiled with dart2wasm (issue #55714).
Fixes a bug in the pub client, such that
dart run
will not interfere withFlutter l10n (at least for most cases) (issue #55758).
v3.4.0
Compare Source
Language
Dart 3.4 makes improvements to the type analysis of conditional expressions
(
e1 ? e2 : e3
), if-null expressions (e1 ?? e2
), if-null assignments(
e1 ??= e2
), and switch expressions (switch (e) { p1 => e1, ... }
). To takeadvantage of these improvements, set your package's
SDK constraint lower bound to 3.4 or greater
(
sdk: '^3.4.0'
).Breaking Change #54640: The pattern context type schema for
cast patterns has been changed from
Object?
to_
(the unknowntype), to align with the specification. This change is not expected
to make any difference in practice.
Breaking Change #54828: The type schema used by the compiler front end
to perform type inference on the operand of a null-aware spread operator
(
...?
) in map and set literals has been made nullable, to match whatcurrently happens in list literals. This makes the compiler front end behavior
consistent with that of the analyzer. This change is expected to be very low
impact.
Libraries
dart:async
ParallelWaitError
to get some meta-information thatit can expose in its
toString
, and theIterable<Future>.wait
and(Future,...,Future).wait
extension methods now provide that information.Should make a
ParallelWaitError
easier to log.dart:cli
waitFor
is removed in 3.4.dart:ffi
Struct.create
andUnion.create
to create struct and union viewsof the sequence of bytes stored in a subtype of
TypedData
.dart:io
Breaking change #53863:
Stdout
has a new fieldlineTerminator
,which allows developers to control the line ending used by
stdout
andstderr
. Classes thatimplement Stdout
must define thelineTerminator
field. The default semantics of
stdout
andstderr
are not changed.Deprecates
FileSystemDeleteEvent.isDirectory
, which always returnsfalse
.dart:js_interop
Fixes an issue with several comparison operators in
JSAnyOperatorExtension
that were declared to return
JSBoolean
but really returnedbool
. This ledto runtime errors when trying to use the return values. The implementation now
returns a
JSBoolean
to align with the interface. See issue #55024 formore details.
Added
ExternalDartReference
and related conversion functionstoExternalReference
andtoDartObject
. This is a faster alternative toJSBoxedDartObject
, but with fewer safety guarantees and fewerinteroperability capabilities. See #55187 for more details.
On dart2wasm,
JSBoxedDartObject
now is an actual JS object that wraps theopaque Dart value instead of only externalizing the value. Like the JS
backends, you'll now get a more useful error when trying to use it in another
Dart runtime.
Added
isA
helper to make type checks easier with interop types. See#54138 for more details.
dart:typed_data
BREAKING CHANGE #53218 #53785: The unmodifiable view classes for
typed data are deprecated.
To create an unmodifiable view of a typed-data object, use the
asUnmodifiableView()
methods added in Dart 3.3:The reason for this change is to allow more flexibility in the implementation
of typed data, so the native and web platforms can use different strategies
to ensure that typed data has good performance.
The deprecated types will be removed in Dart 3.5.
Tools
Analyzer
Improved code completion. Fixed over 50% of completion correctness bugs,
tagged
analyzer-completion-correctness
in the issuetracker.
Support for new annotations introduced in version 1.14.0 of the meta
package.
Support for the [
@doNotSubmit
][@doNotSubmit] annotation, noting that any usage of anannotated member should not be submitted to source control.
Support for the [
@mustBeConst
][@mustBeConst] annotation, which indicates that anannotated parameter only accepts constant arguments.
Linter
unnecessary_library_name
][unnecessary_library_name] lint.missing_code_block_language_in_doc_comment
][missing_code_block_language_in_doc_comment] lint.Compilers
value
""
for alldart.library.foo
strings, wheredart:foo
is not anavailable library. Instead there will only be entries for the available
libraries, like
dart.library.core
, where the value was, and still is,"true"
. This should have no effect onconst bool.fromEnvironment(...)
orconst String.fromEnvironment(...)
without adefaultValue
argument, anargument which was always ignored previously. It changes the behavior of
const bool.hasEnvironment(...)
on such an input, away from always beingtrue
and therefore useless.DevTools
To learn more, check out the release notes for versions
2.32.0 and 2.33.0.
Pub
Dependency resolution and
dart pub outdated
will now surface if a dependencyis affected by a security advisory, unless the advisory is listed under a
ignored_advisories
section in thepubspec.yaml
file. To learn more aboutpub's support for security advisories, visit
dart.dev/go/pub-security-advisories.
path
-dependencies insidegit
-dependencies are now resolved relative to thegit repo.
All
dart pub
commands can now be run from any subdirectory of a project. Pubwill find the first parent directory with a
pubspec.yaml
and operaterelative it.
New command
dart pub unpack
that downloads a package from pub.dev andextracts it to a subfolder of the current directory.
This can be useful for inspecting the code, or playing with examples.
Dart Runtime
Dart VM flags and options can now be provided to any executable generated
using
dart compile exe
via theDART_VM_OPTIONS
environment variable.DART_VM_OPTIONS
should be set to a list of comma-separated flags and optionswith no whitespace. Options that allow for multiple values to be provided as
comma-separated values are not supported (e.g.,
--timeline-streams=Dart,GC,Compiler
).Example of a valid
DART_VM_OPTIONS
environment variable:Dart VM no longer supports external strings:
Dart_IsExternalString
,Dart_NewExternalLatin1String
andDart_NewExternalUTF16String
functions areremoved from Dart C API.
v3.3.4
Compare Source
This is a patch release that:
the enclosing library's
@JS
annotation were actually using the invocation'senclosing library's
@JS
annotation. (issue #55430).v3.3.3
Compare Source
This is a patch release that:
v3.3.2
Compare Source
This is a patch release that:
of their context in the code restored from dill files, causing crashes in the
incremental compiler whenever it restored a typedef from dill such that the
typedef contained a generic function type on its right-hand side (issue
#55158).
resolved in initializers of extension types (issue #55194).
DateTime.timeZoneName
on Windows, which was checking whether current date is in the summer or
standard time rather than checking if the given moment is in the summer or
standard time (issue #55240).
v3.3.1
Compare Source
This is a patch release that:
extension types would fail to compile without an
@JS
annotation on thelibrary (issue #55057).
operand of an
await
expression, unless the extension type itself implementsFuture
(issue #55095).v3.3.0
Compare Source
Language
Dart 3.3 adds extension types to the language. To use them, set your
package's [SDK constraint][language version] lower bound to 3.3 or greater
(
sdk: '^3.3.0'
).Extension types
An extension type wraps an existing type with a different, static-only
interface. It works in a way which is in many ways similar to a class that
contains a single final instance variable holding the wrapped object, but
without the space and time overhead of an actual wrapper object.
Extension types are introduced by extension type declarations. Each
such declaration declares a new named type (not just a new name for the
same type). It declares a representation variable whose type is the
representation type. The effect of using an extension type is that the
representation (that is, the value of the representation variable) has
the members declared by the extension type rather than the members declared
by its "own" type (the representation type). Example:
The declaration
Meters
is an extension type that has representation typeint
. It introduces an implicit constructorMeters(int value);
and agetter
int get value
.m
andm.value
is the very same object, butm
has type
Meters
andm.value
has typeint
. The point is thatm
has the members of
Meters
andm.value
has the members ofint
.Extension types are entirely static, they do not exist at run time. If
o
is the value of an expression whose static type is an extension type
E
with representation type
R
, theno
is just a normal object whoserun-time type is a subtype of
R
, exactly like the value of an expressionof type
R
. Also the run-time value ofE
isR
(for example,E == R
is true). In short: At run time, an extension type is erased to the
corresponding representation type.
A method call on an expression of an extension type is resolved at
compile-time, based on the static type of the receiver, similar to how
extension method calls work. There is no virtual or dynamic dispatch. This,
combined with no memory overhead, means that extension types are zero-cost
wrappers around their representation value.
While there is thus no performance cost to using extension types, there is
a safety cost. Since extension types are erased at compile time, run-time
type tests on values that are statically typed as an extension type will
check the type of the representation object instead, and if the type check
looks like it tests for an extension type, like
is Meters
, it actuallychecks for the representation type, that is, it works exactly like
is int
at run time. Moreover, as mentioned above, if an extension type is used as
a type argument to a generic class or function, the type variable will be
bound to the representation type at run time. For example:
Extension types are useful when you are willing to sacrifice some run-time
encapsulation in order to avoid the overhead of wrapping values in
instances of wrapper classes, but still want to provide a different
interface than the wrapped object. An example of that is interop, where you
may have data that are not Dart objects to begin with (for example, raw
JavaScript objects when using JavaScript interop), and you may have large
collections of objects where it's not efficient to allocate an extra object
for each element.
Other changes
Breaking Change #54056: The rules for private field promotion have
been changed so that an abstract getter is considered promotable if there are
no conflicting declarations. There are no conflicting declarations if
there are no non-final fields, external fields, concrete getters, or
noSuchMethod
forwarding getters with the same name in the same library.This makes the implementation more consistent and allows
type promotion in a few rare scenarios where it wasn't previously allowed.
It is unlikely, but this change could cause a breakage by changing
an inferred type in a way that breaks later code. For example:
Affected code can be fixed by adding an explicit type annotation.
For example, in the above snippet,
var x
can be changed toint? x
.It's also possible that some continuous integration configurations might fail
if they have been configured to treat warnings as errors, because the expanded
type promotion could lead to one of the following warnings:
unnecessary_non_null_assertion
unnecessary_cast
invalid_null_aware_operator
These warnings can be addressed in the usual way, by removing the unnecessary
operation in the first two cases, or changing
?.
to.
in the third case.To learn more about other rules surrounding type promotion,
check out the guide on Fixing type promotion failures.
Libraries
dart:core
String.fromCharCodes
now allowstart
andend
to be after the end ofthe
Iterable
argument, just likeskip
andtake
does on anIterable
.dart:ffi
@Native
can now be used on fields.Native.addressOf
.elementAt
pointer arithmetic extension methods oncore
Pointer
types are now deprecated.Migrate to the new
-
and+
operators instead.@FfiNative
annotation has been removed.Usages should be updated to use the
@Native
annotation.dart:js_interop
like
JSAny
were previously represented using a custom erasure of@staticInterop
types that were compiler-specific. They are now representedas extension types where their representation types are compiler-specific.
This means that user-defined
@staticInterop
types that implementedJSAny
or
JSObject
can no longer do so and need to useJSObject.fromInteropObject
. Going forward, it's recommended to use extensiontypes to define interop APIs. Those extension types can still implement JS
types.
JSArray
andJSPromise
are now generictypes whose type parameter is a subtype of
JSAny?
. Conversions to and fromthese types are changed to account for the type parameters of the Dart or JS
type, respectively.
dart:js_interop
extensionmembers are moved to different extensions on the same type or a supertype to
better organize the API surface. See
JSAnyUtilityExtension
andJSAnyOperatorExtension
for the new extensions. This shouldn't make adifference unless the extension names were explicitly used.
importModule
to allow users to dynamically import modules using the JSimport()
expression.dart:js_interop_unsafe
has
helper to makehasProperty
calls more concise.dart:typed_data
BREAKING CHANGE (https://github.com/dart-lang/sdk/issues/53218) The
unmodifiable view classes for typed data are deprecated. Instead of using the
constructors for these classes to create an unmodifiable view, e.g.
use the new
asUnmodifiableView()
methods:The reason for this change is to allow more flexibility in the implementation
of typed data so the native and web platforms can use different strategies
for ensuring typed data has good performance.
The deprecated types will be removed in a future Dart version.
dart:nativewrappers
base
sothat none of their subtypes can be implemented. Implementing subtypes can lead
to crashes when passing such native wrapper to a native call, as it will try
to unwrap a native field that doesn't exist.
Tools
Dart command line
dart create
command now uses v3 ofpackage:lints
,including multiple new recommended lints by default.
To learn more about the updated collection of lints,
check out the
package:lints
3.0.0 changelog entry.DevTools
To learn more, check out the release notes for versions
2.29.0, 2.30.0,
and 2.31.0.
Wasm compiler (dart2wasm)
dart:js_util
,package:js
, anddart:js
are now disallowed from being imported when compiling with
dart2wasm
. Preferusing
dart:js_interop
anddart:js_interop_unsafe
.Development JavaScript compiler (DDC)
Type arguments of
package:js
interop types are now printed asany
insteadof being omitted. This is simply a change to the textual representation of
package js types that have type arguments. These type arguments are still
completely ignored by the type system at runtime.
Removed "implements <...>" text from the Chrome custom formatter display for
Dart classes. This information provides little value and keeping it imposes an
unnecessary maintenance cost.
Production JavaScript compiler (dart2js)
The
Invocation
that is passed tonoSuchMethod
will no longer have aminified
memberName
, even when dart2js is invoked with--minify
.See #54201 for more details.
Analyzer
pubspec.yaml
files byadding an
# ignore: <diagnostic_id>
comment.dart doc
comment directives are now reported.flutter_style_todos
][flutter_style_todos] lint now has a quick fix.Linter
iterable_contains_unrelated_type
andConfiguration
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