missing_ field_ type_ in_ struct
Fields in struct classes must have an explicitly declared type of 'int', 'double' or 'Pointer'.
Description
#
The analyzer produces this diagnostic when a field in a subclass of
Struct
or
Union
doesn't have a type annotation. Every field must have
an explicit type, and the type must either be
int
,
double
,
Pointer
,
or a subclass of either
Struct
or
Union
.
For more information about FFI, see C interop using dart:ffi.
Example
#
The following code produces this diagnostic because the field
str
doesn't have a type annotation:
import 'dart:ffi';
final class C extends Struct {
external var str;
@Int32()
external int i;
}
Common fixes
#Explicitly specify the type of the field:
import 'dart:ffi';
import 'package:ffi/ffi.dart';
final class C extends Struct {
external Pointer<Utf8> str;
@Int32()
external int i;
}
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.