relational_pattern_operand_type_not_assignable

The constant expression type '{0}' is not assignable to the parameter type '{1}' of the '{2}' operator.

The analyzer produces this diagnostic when the operand of a relational pattern has a type that isn't assignable to the parameter of the operator that will be invoked.

The following code produces this diagnostic because the operand in the relational pattern (0) is an int, but the > operator defined in C expects an object of type C:

class C {
  const C();
​
  bool operator >(C other) => true;
}
​
void f(C c) {
  switch (c) {
    case > 0:
      print('positive');
  }
}

If the switch is using the correct value, then change the case to compare the value to the right type of object:

class C {
  const C();
​
  bool operator >(C other) => true;
}
​
void f(C c) {
  switch (c) {
    case > const C():
      print('positive');
  }
}

If the switch is using the wrong value, then change the expression used to compute the value being matched:

class C {
  const C();
​
  bool operator >(C other) => true;
​
  int get toInt => 0;
}
​
void f(C c) {
  switch (c.toInt) {
    case > 0:
      print('positive');
  }
}