dart是否支持运算符重载

Question

我读到Dart不支持函数重载.它是否支持运算符重载.如果是,那将是善意的,并告诉我如何在一个简单的例子中如何完成它.还有什么优点等我是编程新手.谢谢.

Answer 1

是Dart确实支持运算符重载,使用operator关键字,然后是要重载的运算符.以下示例重载MyClass对象的==运算符:

class MyClass {
  operator ==(MyClass other) {
    // compare this to other
  }
}

几乎所有的Darts内置运算符都可以重载一些值得注意的例外,即赋值运算符= 和引用等价运算符===(不再存在).

至于运算符重载的优点,它允许您重用具有众所周知的语义含义的运算符,例如==或+,用于对象的操作.例如,如果您有一个重载+运算符的Matrix类,那么您可以使用语法m1 + m2而不是更麻烦的m1.plus(m2)添加两个矩阵

Answer 2

当您==在新版本中尝试使用运算符重载时，所选答案不再有效。现在你需要这样做：

class MyClass {
  @override
  bool operator ==(other) {
    // compare this to other
  }
}

但这并不安全。other未指定为类型，可能会发生意外情况。例如：

void main() {
  var a = A(1);
  var b = B(1);
  var result = a == b;
  print(result); //result is true
}

class A {
  A(this.index);

  final int index;

  @override
  bool operator ==(other) => other.index == index;
}

class B {
  B(this.index);

  final int index;
}

所以你可以这样做：

class A {
  A(this.index);

  final int index;

  @override
  bool operator ==(covariant A other) => other.index == index;
}

您需要使用covariant. 因为 Object 重载了==运算符。

或者你可以

测试对象类型：
访问：hash_and_equals

class A {
  A(this.index);

  final int index;

  @override
  bool operator ==(other) => other is A && (other.index == index);

  @override
  int get hashCode => index;
}

Answer 3

要扩展Lars的答案,您还可以使用内联函数语法重载运算符.

class MyClass {
  operator ==(MyClass o) => id == o.id;
}

Answer 4

学习如何使用运算符重载的一个很好的例子是在dart 中处理复数的类：

import 'dart:core';

class Complex {
  final double real;
  final double imaginary;

  Complex({this.real = 0, this.imaginary = 0});

  Complex.ri(this.real, this.imaginary);

  Complex operator +(Complex b) {
    return Complex(
        real: this.real + b.real, imaginary: this.imaginary + b.imaginary);
  }

  Complex operator -(Complex b) {
    return Complex(
        real: this.real - b.real, imaginary: this.imaginary - b.imaginary);
  }

  Complex operator *(Complex b) {
    return Complex(
        real: this.real * b.real - this.imaginary * b.imaginary,
        imaginary: this.real * b.imaginary + this.imaginary * b.real);
  }

  Complex operator /(Complex b) {
    // /sf/answers/2880266301/
    var conjugation = b.conjugate();
    var denominatorRes = b * conjugation;

    // denominator has only real part
    var denominator = denominatorRes.real;
    var nominator = this * conjugation;

    return Complex(
        real: nominator.real / denominator,
        imaginary: nominator.imaginary / denominator);
  }

  bool operator ==(b) {
    return b.real == this.real && b.imaginary == this.imaginary;
  }

  @override
  String toString() {
    return 'Complex(real: ${real}, imaginary: ${imaginary})';
  }
}