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implicit关键字用于声明隐式的用户定义类型转换运算符。(explicit反之)explicit则用于显示转换用户自定义类型。
static implicit operator target_type ( source_type identifier ){......}
隐式转换可以通过消除不必要的类型转换来提高源代码的可读性。但是,因为可以在未指定的情况下发生隐式转换,因此必须注意防止令人不愉快的后果。

一般情况下,隐式转换运算符应当从不引发异常并且从不丢失信息,以便可以在不知晓的情况下安全使用它们。如果转换运算符不能满足那些条件,则应将其标记为 explicit 作为显示转换数据。 

下边是在网上找的几个简单例子

例1

class Digit
    {
        public Digit(double d) { val = d; }
        public double val;
   
        // User-defined conversion from Digit to double
        public static implicit operator double(Digit d)
        {
            return d.val;
        }
        //  User-defined conversion from double to Digit
        public static implicit operator Digit(double d)
        {
            return new Digit(d);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Digit dig = new Digit(7);
            //This call invokes the implicit "double" operator
            double num = dig;
            //This call invokes the implicit "Digit" operator
            Digit dig2 = 12;
            Console.WriteLine("num = {0} dig2 = {1}", num, dig2.val);
            Console.ReadLine();
        }
    }

例2

//基本数据类型到用户自定义类型 
class Distance
{
    private int feet;
    private double inches;

    //默认构造函数 
    public Distance()
    {
        feet = 0;
        inches = 0.0;
    }

    //带有单参数的构造函数              
    public Distance(double metres)
    {
        double f;
        f = 3.28 * metres;
        this.feet = (int)f;
        this.inches = 12 * (f - feet);
    }

    //由一个double隐式构造一个Distance 
    public static implicit operator Distance(double metres)
    {
        return new Distance(metres);
    }

    //由一个Distance显式返回一个double 
    public static explicit operator double(Distance d)
    {
        double metres;
        metres = d.inches / 12 + (double)d.feet;
        return (metres / 3.28);
    }

    public override string ToString()
    {
        return String.Format("{0}英尺{1}英寸 ", this.feet, this.inches);
    }

}

class DistanceDemo
{
    public static void Main()
    {
        Distance d1 = 1.25;
        Console.WriteLine(d1);

        double d = (double)d1;
        Console.WriteLine(d);
    }
}

例3

using System;

namespace Hunts.Keywords
{
    // 定义一个人民币结构。数据类型转换的语法对于结构和类是一样的
    public struct RMB
    {
        // 注意:这些数的范围可能不能满足实际中的使用
        public uint Yuan;
        public uint Jiao;
        public uint Fen;
        public RMB(uint yuan, uint jiao, uint fen)
        {
            if (fen > 9)
            {
                jiao += fen / 10;
                fen = fen % 10;
            }
            if (jiao > 9)
            {
                yuan += jiao / 10;
                jiao = jiao % 10;
            }
            this.Yuan = yuan;
            this.Jiao = jiao;
            this.Fen = fen;
        }

        public override string ToString()
        {
            return string.Format("¥{0}元{1}角{2}分", Yuan, Jiao, Fen);
        }

        // 一些操作
        public static RMB operator +(RMB rmb1, RMB rmb2)
        {
            return new RMB(rmb1.Yuan + rmb2.Yuan, rmb1.Jiao + rmb2.Jiao, rmb1.Fen + rmb2.Fen);
        }

        public static implicit operator float(RMB rmb)
        {
            return rmb.Yuan + (rmb.Jiao / 10.0f) + (rmb.Fen / 100.00f);
        }

        public static explicit operator RMB(float f)
        {
            uint yuan = (uint)f;
            uint jiao = (uint)((f - yuan) * 10);
            uint fen = (uint)(((f - yuan) * 100) % 10);
            return new RMB(yuan, jiao, fen);
        }

        // more
    }

    class App
    {
        static void Main()
        {
            RMB r1, r2, r3, r4;
            // 记得小学时的某次捐款,我把口袋里藏好的一块钱加6张一毛钱以及13个一分钱的硬币都贡献出去了:(
            r1 = new RMB(1, 6, 13);
            // 其实当时其他人都已经交过了,他们总共交了:
            r2 = new RMB(46, 9, 3);
            // 那么加上我的就是:
            r3 = r1 + r2;
            Console.WriteLine("r3 = {0}", r3.ToString());
            // 隐式转换
            float f = r3;
            Console.WriteLine("float f= {0}", f);
            // 显式转换
            r4 = (RMB)f;
            Console.WriteLine("r4 = {0}", r4.ToString());
            //如果不进行显示转换,将出现错误 CS0266: 无法将类型“float”隐式转换为“Hunts.Keywords.RMB”。存在一个显式转换(是否缺少强制转换?)
            Console.Read();
        }
    }
}


出处:http://www.cnblogs.com/chengxiaohui/articles/1914190.html

 
 
 
 posted on 2017-05-24 09:16  Just_Do  阅读(934)  评论(0编辑  收藏