class OnlyEquals {
  final int value;

  OnlyEquals(this.value);

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is OnlyEquals && value == other.value;
}

class OnlyHashCode {
  final String id;

  OnlyHashCode(this.id);

  @override
  int get hashCode => id.hashCode;
}

class Person {
  final String name;

  Person(this.name);

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is Person && name == other.name;

  @override
  int get hashCode => name.hashCode;
}

class Pair {
  final int a;
  final int b;

  Pair(this.a, this.b);

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is Pair && a == other.a && b == other.b;

  @override
  int hashCode => Object.hash(a, b);
}