type_annotation_deferred_class

The deferred type '{0}' can't be used in a declaration, cast, or type test.

The analyzer produces this diagnostic when the type annotation is in a variable declaration, or the type used in a cast (as) or type test (is) is a type declared in a library that is imported using a deferred import. These types are required to be available at compile time, but aren't.

For more information, check out Lazily loading a library.

The following code produces this diagnostic because the type of the parameter f is imported from a deferred library:

import 'dart:io' deferred as io;

void f(io.File f) {}

If you need to reference the imported type, then remove the deferred keyword:

import 'dart:io' as io;

void f(io.File f) {}

If the import is required to be deferred and there's another type that is appropriate, then use that type in place of the type from the deferred library.

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.