Effective C# 原则26：用IComparable和IComparer实现对象的顺序关系

核心提示： Customer c1;Employee e1;if ( ( c1 as IComparable ).CompareTo( e1 )>0 )Console.WriteLine( "Customer one is greater" );当你通过隐式实现ICompar

Customer c1;
Employee e1;
if ( ( c1 as IComparable ).CompareTo( e1 )　>　0 )
　Console.WriteLine( "Customer one is greater" );

当你通过隐式实现IComparable接口而又提供了一个类型安全的比较时，重载版本的强类型比较增加了性能，而且减少了其他人误用CompareTo方法的可能。你还不能看到.Net框架里Sort函数的所有好处，这是因为它还是用接口指针(参见原则19)来访问CompareTo()方法，但在已道两个对象的类型时，代码的性能会好一些。

我们再对Customer 结构做一个小的修改，C#语言可以重载标准的关系运算符，这些应该利用类型安全的CompareTo()方法：

public struct Customer : IComparable
{
　private string _name;
　public Customer( string name )
　{
　　_name = name;
　}
　#region IComparable Members
　// IComparable.CompareTo()
　// This is not type safe. The runtime type
　// of the right parameter must be checked.
　int IComparable.CompareTo( object right )
　{
　　if ( ! ( right is Customer ) )
　　　throw new ArgumentException( "Argument not a customer",
　　　　"right");
　　Customer rightCustomer = ( Customer )right;
　　return CompareTo( rightCustomer );
　}
　// type-safe CompareTo.
　// Right is a customer, or derived from Customer.
　public int CompareTo( Customer right )
　{
　　return _name.CompareTo( right._name );
　}
　// Relational Operators.
　public static bool operator < ( Customer left,
　　Customer right )
　{
　　return left.CompareTo( right ) < 0;
　}
　public static bool operator <=( Customer left,
　　Customer right )
　{
　　return left.CompareTo( right ) <= 0;
　}
　public static bool operator >( Customer left,
　　Customer right )
　{
　　return left.CompareTo( right ) > 0;
　}
　public static bool operator >=( Customer left,
　　Customer right )
　{
　　return left.CompareTo( right ) >= 0;
　}
　#endregion
}