avoid_futureor_void
Avoid using 'FutureOr
This rule is currently experimental and available as of Dart 3.6.
Details
#AVOID using FutureOr<void>
as the type of a result. This type is
problematic because it may appear to encode that a result is either a
Future<void>
, or the result should be discarded (when it is void
).
However, there is no safe way to detect whether we have one or the other
case (because an expression of type void
can evaluate to any object
whatsoever, including a future of any type).
It is also conceptually unsound to have a type whose meaning is something like "ignore this object; also, take a look because it might be a future".
An exception is made for contravariant occurrences of the type
FutureOr<void>
(e.g., for the type of a formal parameter), and no
warning is emitted for these occurrences. The reason for this exception
is that the type does not describe a result, it describes a constraint
on a value provided by others. Similarly, an exception is made for type
alias declarations, because they may well be used in a contravariant
position (e.g., as the type of a formal parameter). Hence, in type alias
declarations, only the type parameter bounds are checked.
A replacement for the type FutureOr<void>
which is often useful is
Future<void>?
. This type encodes that the result is either a
Future<void>
or it is null, and there is no ambiguity at run time
since no object can have both types.
It may not always be possible to use the type Future<void>?
as a
replacement for the type FutureOr<void>
, because the latter is a
supertype of all types, and the former is not. In this case it may be a
useful remedy to replace FutureOr<void>
by the type void
.
BAD:
FutureOr<void> m() {...}
GOOD:
Future<void>? m() {...}
This rule is experimental. It is being evaluated, and it may be changed or removed. Feedback on its behavior is welcome! The main issue is here: https://github.com/dart-lang/linter/issues/4622
Usage
#To enable the avoid_futureor_void
rule,
add avoid_futureor_void
under linter > rules in your
analysis_options.yaml
file:
linter:
rules:
- avoid_futureor_void
除非另有说明,文档之所提及适用于 Dart 3.5.4 版本,本页面最后更新时间: 2024-08-02。 查看文档源码 或者 报告页面问题。