EffectiveC#18--用IComparable和IComparer实现对象的顺序关系

1..Net框架提供了接口来描述对象的顺序关系：IComparable 和IComparer。

2.IComparable 为类定义了自然顺序，实现IComparer接口的类可以描述其它可选的顺序

3.原因：避免在运行时默认比较关系的低效

4.IComparable接口只有一个方法：CompareTo()  ，建议进行如下的实现而不是实现一个Compareto公共方法接受的却是object类型参数，因为这样会不停的装箱拆箱

注意：IComparable.CompareTo()是一个隐式的接口实现它，只能通过IComparable 接口的引用才能调用

public struct Customer : IComparable
{ 
  private string _name;
  public Customer( string name ) { _name = name; }

  int IComparable.CompareTo( object right )
  {
   if ( ! ( right is Customer ) )
       throw new ArgumentException( "Argument not a customer", "right" ); 
   Customer rightCustomer = ( Customer )right; return CompareTo( rightCustomer );
  }
  public int CompareTo( Customer right )
  { return _name.CompareTo( right._name ); } 
}
//作者建议重写比较运算符
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; }