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

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

Example

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
*/

Robust Programming

• 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.

See Also

Reference

Conversion Operators (C# Programming Guide)

Concepts

C# Programming Guide

Other Resources

C# Reference