When should I define a (explicit or implicit) conversion operator in C#? [closed]

Question

A somewhat little-known feature of C# is the possibility to create implicit or explicit user-defined type conversions. I have been writing C# code for 6 years now, and I have never used it. So, I'm afraid I might be missing good opportunities.

What are legitimate, good uses of user-defined conversions? Do you have examples where they are better than just defining a custom method?

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Turns out, Microsoft has some design guidelines about conversions, the most relevant of which is:

Do not provide a conversion operator if such conversion is not clearly expected by the end users.

But when is a conversion "expected"? Outside of toy number classes, I can't figure out any real-world use case.

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Here's a summary of the examples provided in the answers:

• Radians/Degrees/double
• Polar/Point2D
• Kelvin/Farenheit/Celsius

The pattern seems to be: implicit conversions are mostly (only?) useful when defining numerical/value types, the conversion being defined by a formula. In retrospect this is kind of obvious. Still, I wonder if non-numerical classes could also benefit from implicit conversions..?

Answer 1

You can use a conversion operator when there is a natural and clear conversion to or from a different type.

Say for example that you have a data type for representing temperatures:

public enum TemperatureScale { Kelvin, Farenheit, Celsius }

public struct Temperature {

  private TemperatureScale _scale;
  private double _temp;

  public Temperature(double temp, TemperatureScale scale) {
    _scale = scale;
    _temp = temp;
  }

  public static implicit operator Temperature(double temp) {
    return new Temperature(temp, TemperatureScale.Kelvin);
  }

}

Using the implicit operator you can assign a double to a temperature variable, and it will automatically be used as Kelvin:

Temperature a = new Temperature(100, TemperatureScale.Celcius);
Temperature b = 373.15; // Kelvin is default