illegal_concrete_enum_member

A concrete instance member named '{0}' can't be declared in a class that implements 'Enum'.

A concrete instance member named '{0}' can't be inherited from '{1}' in a class that implements 'Enum'.

The analyzer produces this diagnostic when either an enum declaration, a class that implements Enum, or a mixin with a superclass constraint of Enum, declares or inherits a concrete instance member named either index, hashCode, or ==.

The following code produces this diagnostic because the enum E declares an instance getter named index:

enum E {
  v;
​
  int get index => 0;
}

The following code produces this diagnostic because the class C, which implements Enum, declares an instance field named hashCode:

abstract class C implements Enum {
  int hashCode = 0;
}

The following code produces this diagnostic because the class C, which indirectly implements Enum through the class A, declares an instance getter named hashCode:

abstract class A implements Enum {}
​
abstract class C implements A {
  int get hashCode => 0;
}

The following code produces this diagnostic because the mixin M, which has Enum in the on clause, declares an explicit operator named ==:

mixin M on Enum {
  bool operator ==(Object other) => false;
}

Rename the conflicting member:

enum E {
  v;
​
  int get getIndex => 0;
}