Dart 比较运算符

Question

我在做一个测量类，所以我想提供一个很好的 API 来比较两个测量值。

为了处理集合中的排序，我实现了Comparator。对于一个不错的 API，我还实现了比较运算符 <、<=、=>、>、==。

所以我的班级有以下方法：

bool operator <=(SELF other) => _value <= other._value;

bool operator <(SELF other) => _value < other._value;

bool operator >(SELF other) => _value > other._value;

bool operator >=(SELF other) => _value >= other._value;

@override
bool operator ==(Object other) =>
    identical(this, other) || other is UnitValue && runtimeType == other.runtimeType && _value == other._value;

@override
int get hashCode => _value.hashCode;

int compareTo(SELF other) => _value.compareTo(other._value);

感觉我不得不添加太多样板代码。 Dart 是否提供任何混合以基于运算符子集获得所有实现？

Answer 1

我不这么认为...但是您可以使用简单的 mixin 来实现基于 Comparable 实现的运算符：

mixin Compare<T> on Comparable<T> {
  bool operator <=(T other) => this.compareTo(other) <= 0;

  bool operator >=(T other) => this.compareTo(other) >= 0;

  bool operator <(T other) => this.compareTo(other) < 0;

  bool operator >(T other) => this.compareTo(other) > 0;

  bool operator ==(other) => other is T && this.compareTo(other) == 0;
}

示例用法：

class Vec with Comparable<Vec>, Compare<Vec> {
  final double x;
  final double y;

  Vec(this.x, this.y);

  @override
  int compareTo(Vec other) =>
      (x.abs() + y.abs()).compareTo(other.x.abs() + other.y.abs());
}

main() {
  print(Vec(1, 1) > Vec(0, 0));
  print(Vec(1, 0) > Vec(0, 0));
  print(Vec(0, 0) == Vec(0, 0));
  print(Vec(1, 1) <= Vec(2, 0));
}