const_map_key_not_primitive_equality

The type of a key in a constant map can't override the '==' operator, or 'hashCode', but the class '{0}' does.

The analyzer produces this diagnostic when the class of object used as a key in a constant map literal implements either the == operator, the getter hashCode, or both. The implementation of constant maps uses both the == operator and the hashCode getter, so any implementation other than the ones inherited from Object requires executing arbitrary code at compile time, which isn't supported.

The following code produces this diagnostic because the constant map contains a key whose type is C, and the class C overrides the implementation of ==:

class C {
  const C();

  bool operator ==(Object other) => true;
}

const map = {C() : 0};

The following code produces this diagnostic because the constant map contains a key whose type is C, and the class C overrides the implementation of hashCode:

class C {
  const C();

  int get hashCode => 3;
}

const map = {C() : 0};

If you can remove the implementation of == and hashCode from the class, then do so:

class C {
  const C();
}

const map = {C() : 0};

If you can't remove the implementation of == and hashCode from the class, then make the map non-constant:

class C {
  const C();

  bool operator ==(Object other) => true;
}

final map = {C() : 0};

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.