Student : IComparable<Student> 以及逆变和协变
IComparable<Student>是Student的父类,所以IComparable<Student>可以接收Student。
但是在使用CompareTo方法的时候,必须传入Student,不允许传入父类IComparable<Student>。
public interface IComparable<in T>, in关键字表示逆变Contravariance,Enables you to use a more generic (less derived) type than originally specified
//Contravariance, Enables you to use a more generic (less derived) type than originally specified. 用来做函数参数 //public delegate void Action<in T>(T obj) Action<Base> actionBase = ActionMethod; Action<Derived> actionDerived = actionBase; actionDerived(new Derived());
public class Student : IComparable<Student> { public int Id { get; set; } public int CompareTo(Student other) { return Id - other.Id; } } class Test { public Test() { IComparable<Student> student1 = new Student() {Id = 1}; IComparable<Student> student2 = new Student() {Id = 2}; int result = student1.CompareTo(student2); } }
修改成下面的代码就可以了,使用var关键字,让编译自动推断类型
[TestFixture] public class TestHelper { [Test] public void Test() { var student1 = new Student() { Id = 1 }; var student2 = new Student() { Id = 2 }; int result = student1.CompareTo(student2); Console.WriteLine(result); } }