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implicit (C# Reference)

The implicit keyword is used to declare an implicit user-defined type conversion operator. Use it to enable implicit conversions between a user-defined type and another type, if the conversion is guaranteed not to result in a loss of data.

    class Digit
    {
        public Digit(double d) { val = d; }
        public double val;
        // ...other members

        // 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();
        }
    }

By eliminating unnecessary casts, implicit conversions can improve source code readability. However, because implicit conversions do not require programmers to explicitly cast from one type to the other, care must be taken to prevent unexpected results. In general, implicit conversion operators should never throw exceptions and never lose information so that they can be used safely without the programmer's awareness. If a conversion operator cannot meet those criteria, it should be marked explicit. For more information, see Using Conversion Operators.

For more information, see the following section in the C# Language Specification:

  • 6.1 Implicit conversions

  • 10.9.3 Conversion Operators

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