Operator Overloading

C#中操作符都是一些静态方法,其返回值表示操作结果,其参数是操作数. 当要为一个类创建操作符时,称之为重载(overload)该操作符,比如要重载操作符"+",应该写成:

public static Fraction operator+(Fraction lop, Fraction rop)

 

如果重载了==操作符,必须同时重载不等于!=.(编译器还希望重定义GetHashCode,否则会有警告). 同样<,>,<=,>=这几个操作符也必须成对定义.

 

隐式转换,显式转换

 

隐式转换不会丢失信息,而显式转换则可能导致信息的丢失,比如将long型数据转换成int型等等...

 

对我们自己定义的类型的数据是如何实现转换的呢?

同样分隐式转换和显式转换,当转换肯定成功且不会丢失信息时,加上前缀的关键字implicit,否则就加上关键字 explicit.

看下面的例子

using System;namespace Conversions{ public class Fraction { private int numerator; private int denominator; public Fraction(int numerator, int denominator) { Console.WriteLine("In Fraction Constructor(int, int)"); this.numerator = numerator; this.denominator = denominator; } public Fraction(int wholeNumber) { Console.WriteLine("In Fraction Constructor(int)"); numerator = wholeNumber; denominator = 1; } public static implicit operator Fraction(int theInt) { Console.WriteLine("In implicit conversion to Fraction"); return new Fraction(theInt); } public static explicit operator int(Fraction theFraction) { Console.WriteLine("In explicit conversion to int"); return theFraction.numerator / theFraction.denominator; } public static bool operator ==(Fraction lhs, Fraction rhs) { Console.WriteLine("In operator =="); if (lhs.denominator == rhs.denominator && lhs.numerator == rhs.numerator) { return true; } // code here to handle unlike fractions return false; } public static bool operator !=(Fraction lhs, Fraction rhs) { Console.WriteLine("In operator !="); return !(lhs == rhs); } public override bool Equals(object o) { Console.WriteLine("In method Equals"); if (!(o is Fraction)) { return false; } return this == (Fraction)o; } public static Fraction operator +(Fraction lhs, Fraction rhs) { Console.WriteLine("In operator+"); if (lhs.denominator == rhs.denominator) { return new Fraction(lhs.numerator + rhs.numerator, lhs.denominator); } // simplistic solution for unlike fractions // 1/2 + 3/4 == (1*4) + (3*2) / (2*4) == 10/8 int firstProduct = lhs.numerator * rhs.denominator; int secondProduct = rhs.numerator * lhs.denominator; return new Fraction( firstProduct + secondProduct, lhs.denominator * rhs.denominator ); } public override string ToString() { String s = numerator.ToString() + "/" + denominator.ToString(); return s; } } class Program { static void Main(string[] args) { Fraction f1 = new Fraction(3, 4); Console.WriteLine("f1: {0}", f1.ToString()); Fraction f2 = new Fraction(2, 4); Console.WriteLine("f2: {0}", f2.ToString()); Fraction f3 = f1 + f2; Console.WriteLine("f1 + f2 = f3: {0}", f3.ToString()); Fraction f4 = f3 + 5; Console.WriteLine("f3 + 5 = f4: {0}", f4.ToString()); Fraction f5 = new Fraction(2, 4); if (f5 == f2) { Console.WriteLine("F5: {0} == F2: {1}", f5.ToString(), f2.ToString()); } } }}

上面代码中需要注意的是两个转换操作符的声明,第一个转换操作符将int转换为fraction:

 public static implicit operator Fraction(int theInt)
    {
        Console.WriteLine("In implicit conversion to Fraction");
        return new Fraction(theInt);
    }

 这个转换是被标记为implicit的,因为从整数到分数,只需要把分母设为1,分子设为该整数就可以转换为分数,不会造成任何截断.

 

第二个转换操作符用于fraction到int的显式转换:

public static explicit operator int(Fraction theFraction)
        {
            Console.WriteLine("In explicit conversion to int");
            return theFraction.numerator /
            theFraction.denominator;
        }