subtype_ of_ ffi_ class
The class '{0}' can't extend '{1}'.
The class '{0}' can't implement '{1}'.
The class '{0}' can't mix in '{1}'.
Description
#
The analyzer produces this diagnostic when a class extends any FFI class
other than Struct
or Union
, or implements or mixes in any FFI class.
Struct
and Union
are the only FFI classes that can be subtyped, and
then only by extending them.
For more information about FFI, see C interop using dart:ffi.
Example
#
The following code produces this diagnostic because the class C
extends
Double
:
import 'dart:ffi';
final class C extends Double {}
Common fixes
#
If the class should extend either Struct
or Union
, then change the
declaration of the class:
import 'dart:ffi';
final class C extends Struct {
@Int32()
external int i;
}
If the class shouldn't extend either Struct
or Union
, then remove any
references to FFI classes:
final class C {}
Unless stated otherwise, the documentation on this site reflects Dart 3.9.2. Page last updated on 2025-9-1. View source or report an issue.