packed_annotation_alignment

Only packing to 1, 2, 4, 8, and 16 bytes is supported.

The analyzer produces this diagnostic when the argument to the Packed annotation isn't one of the allowed values: 1, 2, 4, 8, or 16.

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

The following code produces this diagnostic because the argument to the Packed annotation (3) isn't one of the allowed values:

import 'dart:ffi';

@Packed(3)
final class C extends Struct {
  external Pointer<Uint8> notEmpty;
}

Change the alignment to be one of the allowed values:

import 'dart:ffi';

@Packed(4)
final class C extends Struct {
  external Pointer<Uint8> notEmpty;
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.