await_ of_ incompatible_ type
The 'await' expression can't be used for an expression with an extension type that is not a subtype of 'Future'.
Description
#
The analyzer produces this diagnostic when the type of the expression in
an
await
expression is an extension type, and the extension type isn't a
subclass of
Future
.
Example
#
The following code produces this diagnostic because the extension type
E
isn't a subclass of
Future
:
extension type E(int i) {}
void f(E e) async {
await e;
}
Common fixes
#If the extension type is correctly defined, then remove the await
:
extension type E(int i) {}
void f(E e) {
e;
}
If the extension type is intended to be awaitable, then add
Future
(or a
subtype of
Future
) to the
implements
clause (adding an
implements
clause if there isn't one already), and make the representation type
match:
extension type E(Future<int> i) implements Future<int> {}
void f(E e) async {
await e;
}
Unless stated otherwise, the documentation on this site reflects Dart 3.9.2. Page last updated on 2025-9-4. View source or report an issue.