How to: Implement User-Defined Conversions Between Structs (C# Programming Guide)

 

Updated: July 20, 2015

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

This example defines two structs, RomanNumeral and BinaryNumeral, and demonstrates conversions between them.

        struct RomanNumeral
        {
            private int value;

            public RomanNumeral(int value)  //constructor
            {
                this.value = value;
            }

            static public implicit operator RomanNumeral(int value)
            {
                return new RomanNumeral(value);
            }

            static public implicit operator RomanNumeral(BinaryNumeral binary)
            {
                return new RomanNumeral((int)binary);
            }

            static public explicit operator int(RomanNumeral roman)
            {
                return roman.value;
            }

            static public implicit operator string(RomanNumeral roman)
            {
                return ("Conversion to string is not implemented");
            }
        }

        struct BinaryNumeral
        {
            private int value;

            public BinaryNumeral(int value)  //constructor
            {
                this.value = value;
            }

            static public implicit operator BinaryNumeral(int value)
            {
                return new BinaryNumeral(value);
            }

            static public explicit operator int(BinaryNumeral binary)
            {
                return (binary.value);
            }

            static public implicit operator string(BinaryNumeral binary)
            {
                return ("Conversion to string is not implemented");
            }
        }

        class TestConversions
        {
            static void Main()
            {
                RomanNumeral roman;
                BinaryNumeral binary;

                roman = 10;

                // Perform a conversion from a RomanNumeral to a BinaryNumeral:
                binary = (BinaryNumeral)(int)roman;

                // Perform a conversion from a BinaryNumeral to a RomanNumeral:
                // No cast is required:
                roman = binary;

                System.Console.WriteLine((int)binary);
                System.Console.WriteLine(binary);

                // Keep the console window open in debug mode.
                System.Console.WriteLine("Press any key to exit.");
                System.Console.ReadKey();
            }
        }
        /* Output:
            10
            Conversion not yet implemented
        */

  • In the previous example, the statement:

                    binary = (BinaryNumeral)(int)roman;
    

    performs a conversion from a RomanNumeral to a BinaryNumeral. Because there is no direct conversion from RomanNumeral to BinaryNumeral, a cast is used to convert from a RomanNumeral to an int, and another cast to convert from an int to a BinaryNumeral.

  • Also the statement

                    roman = binary;
    

    performs a conversion from a BinaryNumeral to a RomanNumeral. Because RomanNumeral defines an implicit conversion from BinaryNumeral, no cast is required.

C# Reference
C# Programming Guide
Conversion Operators

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