public static Fahrenheit ToFahrenheit(this Celsius celsius)
{
return(new Fahrenheit(celsius.Value * 9 / 5 + 32));
}
/*
* Extension methods are a powerful tool in C#, but they must
* be used wisely. They're well suited to adding utility to existing
* classes that you may not be able to alter directly (such as framework
* classes). This can help a lot with avoiding static utility methods and
* helper classes which makes the calling code feel more object-oriented and
* less procedural, reducing complexity in the process. However, they shouldn't
* be used in all cases. Extension methods should never be used when they would rely
* on the internal state of a class they're extending (beyond public getters).
* They also can make classes harder to mock. If you were to add an extension method
* to, say, `IFoo`:
*
* public static void Bar(this IFoo foo){
* Console.Writeline(foo);
* }
*
* Note the `this` keyword. That keyword is what marks the signature as an extension method.
* Extension methods must be static, the first parameter must be an instance of the type being
* extended preceded by `this`, and they must be contained within a static class.
*
* If, during unit testing, you create a mock object, you'll find not all
* mocking frameworks will capture your extension method.
*
* Some of the best candidates for extension methods are to extend the capabilities of a class
* that you are not responsible for testing.
*
* Extension methods are also used heavily by 3rd party libraries (and even
* the framework itself) to provide registration methods for various features.
* The `AddControllers()` method in `Startup.cs`, for example, is an extension method
* on the `IServiceCollection` class. It's very common to write extension methods
* to expose middleware or even just cleanly register whatever types your library needs
* with the DI framework.
*/
public static Kelvin ToKelvin(this Celsius celsius)
{
return(new Kelvin(celsius.Value + (decimal)273.15));
}