delegate T Factory<out R, in S , T>()
// out R 协变 in S 逆变 T 不变
----------------------------------------------------------------------------------------------------
public delegate TR Func<T1, T2, TR>(T1 p1, T2 p2); //泛型委托 TR委托返回类型 T1，T2 委托参数类型
class Simple
{
static public string PrintString(int p1, int p2) //方法匹配委托
{
int total = p1 + p2;
return total.ToString();
}
}
class Program
{
static void Main()
{
var myDel = new Func <int, int, string>(Simple.PrintString); //创建委托实例
Console.WriteLine("ToTal: {0}", myDel(15, 13));// 调用委托
}
}
另一种out协变
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication33
{
class Animal //基类
{
public int Legs = 4;
}
class Dog:Animal //派生类
{
}
class Program
{
delegate T Factory<out T>();
static Dog MackDog() { return new Dog(); }
static void Main(string[] args)
{
Factory<Animal> animalMacker = MackDog; //隐式强制转换
Factory<Dog> dogMacker = MackDog;
Factory<Animal> animalMacker2 = dogMacker; //需要out标识符
Factory<Animal> animalMacker3 = new Factory<Dog>(MackDog); //需要out标识符
}
}
}