C# 运算符重载完全指南：自定义类型的运算符行为定义

C# 允许重定义或重载大多数内置运算符，使程序员能将运算符用于用户定义类型。重载运算符是特殊名称的函数：operator 关键字后跟运算符符号。与其他函数一样，有返回类型和参数列表。

运算符重载实现

以 Box 类为例，重载加法运算符 +：

public static Box operator+ (Box b, Box c) {
    Box box = new Box();
    box.length = b.length + c.length;
    box.breadth = b.breadth + c.breadth;
    box.height = b.height + c.height;
    return box;
}

该函数实现两个 Box 对象相加，返回新的 Box 对象。

完整实现示例

using System;
namespace OperatorOvlApplication {
    class Box {
        private double length, breadth, height;
        
        public double getVolume() { return length * breadth * height; }
        public void setLength(double len) { length = len; }
        public void setBreadth(double bre) { breadth = bre; }
        public void setHeight(double hei) { height = hei; }
        
        // 重载 + 运算符
        public static Box operator+ (Box b, Box c) {
            Box box = new Box();
            box.length = b.length + c.length;
            box.breadth = b.breadth + c.breadth;
            box.height = b.height + c.height;
            return box;
        }
    }
    
    class Tester {
        static void Main(string[] args) {
            Box Box1 = new Box(), Box2 = new Box(), Box3 = new Box();
            double volume = 0.0;
            
            Box1.setLength(6.0); Box1.setBreadth(7.0); Box1.setHeight(5.0);
            Box2.setLength(12.0); Box2.setBreadth(13.0); Box2.setHeight(10.0);
            
            volume = Box1.getVolume();
            Console.WriteLine("Volume of Box1 : {0}", volume);  // 210
            
            volume = Box2.getVolume();
            Console.WriteLine("Volume of Box2 : {0}", volume);  // 1560
            
            // 使用重载的 + 运算符
            Box3 = Box1 + Box2;
            volume = Box3.getVolume();
            Console.WriteLine("Volume of Box3 : {0}", volume);  // 5400
            Console.ReadKey();
        }
    }
}

可重载与不可重载运算符

扩展示例：重载比较运算符与 ToString

public static bool operator == (Box lhs, Box rhs) {
    return lhs.length == rhs.length && lhs.height == rhs.height && lhs.breadth == rhs.breadth;
}

public static bool operator != (Box lhs, Box rhs) {
    return !(lhs == rhs);  // 建议复用 == 实现
}

public static bool operator < (Box lhs, Box rhs) {
    return lhs.length < rhs.length && lhs.height < rhs.height && lhs.breadth < rhs.breadth;
}

public static bool operator > (Box lhs, Box rhs) {
    return lhs.length > rhs.length && lhs.height > rhs.height && lhs.breadth > rhs.breadth;
}

public static bool operator <= (Box lhs, Box rhs) {
    return lhs == rhs || lhs < rhs;
}

public static bool operator >= (Box lhs, Box rhs) {
    return lhs == rhs || lhs > rhs;
}

public override string ToString() {
    return String.Format("({0}, {1}, {2})", length, breadth, height);
}

测试代码

Box Box1 = new Box(); Box1.setLength(6); Box1.setBreadth(7); Box1.setHeight(5);
Box Box2 = new Box(); Box2.setLength(12); Box2.setBreadth(13); Box2.setHeight(10);
Box Box3 = Box1 + Box2;
Box Box4 = Box3;

Console.WriteLine("Box 1: {0}", Box1);  // (6, 7, 5)
Console.WriteLine("Box 2: {0}", Box2);  // (12, 13, 10)
Console.WriteLine("Box 3: {0}", Box3);  // (18, 20, 15)

Console.WriteLine(Box1 > Box2 ? "Box1 > Box2" : "Box1 <= Box2");  // Box1 <= Box2
Console.WriteLine(Box1 < Box2 ? "Box1 < Box2" : "Box1 >= Box2");  // Box1 < Box2
Console.WriteLine(Box3 == Box4 ? "Box3 == Box4" : "Box3 != Box4");  // Box3 == Box4

重载规则与最佳实践

• 重载运算符必须声明为 public static
• 一元运算符一个参数，二元运算符两个参数（至少一个为包含类型）
• 比较运算符必须成对重载（== 与 !=、< 与 >、<= 与 >=）
• 重载 == 时应重写 Equals() 和 GetHashCode()
• 避免重载运算符产生非直观行为（如 + 做减法）
• 结构体重载运算符需注意值类型拷贝语义