Working with the Framework - Effective C# - page 187

public static bool operator >=( Customer left,
Customer right)
{
return left.CompareTo(right) >= 0 ;
}
}
That's all for the standard order of customers: by name. Later, you must
create a report sorting all customers by revenue. You still need the normal
comparison functionality defined by the Customer struct , sorting them
by name. Most APIs developed after generics became part of the .NET
Framework will ask for a Comparison<T> delegate to perform some other
sort. It's simple to create static properties in the Customer type that pro-
vide other comparison orders. For example, this delegate compares the
revenue generated by two customers:
public static Comparison < Customer > CompareByReview
{
get
{
return (left,right) =>
left.revenue.CompareTo(right.revenue);
}
}
Older libraries will ask for this kind of functionality using the IComparer
interface. IComparer provides the standard way to provide alternative
orders for a type without using generics. Any of the methods delivered in
the 1.x .NET FCL that work on IComparable types provide overloads that
order objects through IComparer. Because you authored the Customer
struct , you can create this new class (RevenueComparer) as a private
nested class inside the Customer struct . It gets exposed through a static
property in the Customer struct :
public struct Customer : IComparable < Customer >, IComparable
{
private readonly string name;
private double revenue;
public Customer( string name, double revenue)
{
this .name = name;