来源

import "dart:math";

abstract class Shape<T> {
  T getArea();
}

class Circle<T> extends Shape<T> {
  T radius;
  Circle({required this.radius});

  @override
  T getArea() => radius * radius * pi;
}

class Square<T> extends Shape<T> {
  T length;

  Square({required this.length});

  @override
  T getArea() => length! * length!;
}

void main() {
  Circle circle = Circle(radius: 0);
  print(circle.getArea());

  Circle circle2 = Circle(radius: 10);
  print(circle2.getArea());

  Square square = Square(length: 20.0);
  print(square.getArea());
}

dart编译器生成Error：

Error: The operator '*' isn't defined for the class 'Object'.
 - 'Object' is from 'dart:core'.
Try correcting the operator to an existing operator, or defining a '*' operator.

如何在Dart中使用泛型类型支持基本arithmetic operators？