avoid_futureor_void

Avoid using 'FutureOr' as the type of a result.

此规则目前处于 experimental 状态，自 Dart 3.6 版本起可用。

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

要启用 avoid_futureor_void 规则，请在你的 analysis_options.yaml 文件中，在 linter > rules 下添加 avoid_futureor_void ：

linter:
  rules:
    - avoid_futureor_void

除非另有说明，否则本网站上的文档反映的是 Dart 3.6.0。页面最后更新于 2025-02-05。 查看源代码 或 报告问题.