Building comparable types

IComparable Interface defines a generalized type-specific comparison method that a value type or class implements to order or sort its instances.

This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo(Object), that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. The instance's IComparable implementation is called automatically by methods such as Array.Sort and ArrayList.Sort.

The implementation of the CompareTo(Object) method must return an Int32 that has one of three values, as shown in the following table.

Value	Meaning
Less than zero	The current instance precedes the object specified by the CompareTo method in the sort order.
Zero	This current instance occurs in the same position in the sort order as the object specified by the CompareTo method.
Greater than zero	This current instance follows the object specified by the CompareTo method in the sort order.

All numeric types (such as Int32 and Double) implement IComparable, as do String, Char, and DateTime. Custom types should also provide their own implementation of IComparable to enable object instances to be ordered or sorted.

public class Temperature : IComparable 
{
    // The temperature value
    protected double temperatureF;

    public int CompareTo(object obj) {
        if (obj == null) return 1;
        
        Temperature otherTemperature = obj as Temperature;
        if (otherTemperature != null) 
            return this.temperatureF.CompareTo(otherTemperature.temperatureF);
        else
           throw new ArgumentException("Object is not a Temperature");
    }
}