flutter - Dart语言演练-覆盖问题

Question

尽管Dart Language Walk中的此代码段失败了。请参阅here下有关可重写运算符的部分。知道为什么吗？

  class Vector {
   final int x, y;
  
   Vector(this.x, this.y);
  
   Vector operator +(Vector v) => Vector(x + v.x, y + v.y);
   Vector operator -(Vector v) => Vector(x - v.x, y - v.y);
   // use this and the assert will work
   // bool operator ==(Vector v) => x == v.x && y == v.y;
   // See encubus accepted answer below.

  
   Dump() {
     print(this.x);
     print(this.y);
   }


   // Operator == and hashCode not shown. For details, see note below.
   // ···
  }

  final v = Vector(2, 3);
  final w = Vector(2, 2);

  var x = v+w;
  x.dump();
  assert(x == Vector(4,5));
  assert((v + w) == Vector(4, 5));

所有的断言都失败了，但是x.dump()的输出是4和5。我修改了代码以在v + w周围添加()，以便在只声明w而没有断言的情况下检查+覆盖的结果。和。

Answer 1

没有为Vector类重新定义==运算符

// Operator == and hashCode not shown.

您需要为 ==类实现 Vector才能使用它。
https://api.dart.dev/be/175383/dart-core/Object/operator_equals.html
https://api.dart.dev/be/175383/dart-core/Object/hashCode.html
如果子类覆盖了相等运算符，则它也应该覆盖hashCode方法，以保持一致性。