non_sized_type_argument

The type '{1}' isn't a valid type argument for '{0}'. The type argument must be a native integer, 'Float', 'Double', 'Pointer', or subtype of 'Struct', 'Union', or 'AbiSpecificInteger'.

The analyzer produces this diagnostic when the type argument for the class Array isn't one of the valid types: either a native integer, Float, Double, Pointer, or subtype of Struct, Union, or AbiSpecificInteger.

For more information about FFI, see C interop using dart:ffi.

The following code produces this diagnostic because the type argument to Array is Void, and Void isn't one of the valid types:

import 'dart:ffi';

final class C extends Struct {
  @Array(8)
  external Array<Void> a0;
}

Change the type argument to one of the valid types:

import 'dart:ffi';

final class C extends Struct {
  @Array(8)
  external Array<Uint8> a0;
}

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.