当我试图从Jon Skeet的书C#深入调整清单3.4时,我收到以下错误消息…
The type ‘list_3_4.Dog’ cannot be used as type parameter ‘T’ in the generic type or method ‘list_3_4.Program.CompareToDefault(T)’.
There is no implicit reference conversion from ‘list_3_4.Dog’ to ‘System.IComparable’.
这是我的代码……
using System;
namespace list_3_4
{
class Program
{
static void Main(string[] args)
{
//string mystring;
Dog d = new Dog("howie");
Console.WriteLine(CompareToDefault("x"));
Console.WriteLine(CompareToDefault(10));
Console.WriteLine(CompareToDefault(0));
Console.WriteLine(CompareToDefault(-10));
Console.WriteLine(CompareToDefault(DateTime.MinValue));
Console.WriteLine(CompareToDefault(d));
Console.ReadKey();
}
static int CompareToDefault<T> (T value) where T: IComparable<T>
{
return value.CompareTo(default(T));
}
}
public class Dog
{
private string _name;
public Dog(string name)
{
_name = name;
}
}
}
如何添加像“狗”这样的引用类型来使用Jon Skeets代码列表???我知道Dog需要实现IComparable但我不知道怎么做！
解决方法
您可以通过说明需要类型T来定义方法,类型T是IComparable< T>. ：
where T: IComparable<T>
但Dog没有实现IComparable< Dog>
你需要这样做：
public class Dog : IComparable<Dog>
{
//this will allow you to do a quick name comparison
public string Name { get; set;}
public int CompareTo(Dog other)
{//compare dogs by name
return this._name.CompareTo(other.Name);
}
}
注意：对于引用类型,default(T)将返回null,因此您应该在某处执行null检查.阅读约default on msdn.
