Switch case expression type can't override the '==' operatorDRT-W1249

The analyzer produces this diagnostic when the type of the expression following the keyword case has an implementation of the == operator other than the one in Object.

Example

The following code produces this diagnostic because the expression following the keyword case (C(0)) has the type C, and the class C overrides the == operator:

class C {
  final int value;

  const C(this.value);

  bool operator ==(Object other) {
    return false;
  }
}

void f(C c) {
  switch (c) {
    case C(0):
      break;
  }
}

Common fixes

If there isn't a strong reason not to do so, then rewrite the code to use an if-else structure:

class C {
  final int value;

  const C(this.value);

  bool operator ==(Object other) {
    return false;
  }
}

void f(C c) {
  if (c == C(0)) {
    // ...
  }
}

If you can't rewrite the switch statement and the implementation of == isn't necessary, then remove it:

class C {
  final int value;

  const C(this.value);
}

void f(C c) {
  switch (c) {
    case C(0):
      break;
  }
}

If you can't rewrite the switch statement and you can't remove the definition of ==, then find some other value that can be used to control the switch:

class C {
  final int value;

  const C(this.value);

  bool operator ==(Object other) {
    return false;
  }
}

void f(C c) {
  switch (c.value) {
    case 0:
      break;
  }
}