c# implicit explicit关键字(隐式和显式数据类型转换)

implicit

　　Implicit关键字用于声明隐式的用户定义类型转换运算符。它可以实现2个不同类的隐式转换 ，提高代码的可读性。但是需要注意使用隐式转换操作符之后，在编译时会跳过异常检查，所以隐式转换运算符应当从不引发异常并且从不丢失信息，否则在运行时会出现一些意想不到的问题。

    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();
        }
    }

Explicit

　　Explicit关键字声明必须通过转换来调用的用户定义的类型转换运算符。不同于隐式转换，显式转换运算符必须通过转换的方式来调用，如果缺少了显式的转换，在编译时就会产生错误。　

    class Digit
    {
        public Digit(double d) { val = d; }
        public double val;

        // User-defined conversion from Digit to double
        public static explicit operator double(Digit d)
        {
            return d.val;
        }
        //  User-defined conversion from double to Digit
        public static explicit 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 = (double)dig;
            //This call invokes the implicit "Digit" operator
            Digit dig2 = (Digit)12;
            Console.WriteLine("num = {0} dig2 = {1}", num, dig2.val);
            Console.ReadLine();
        }
    }