C# 使用泛型协变性

在 C# 中处理多个类型的生产者时，可以使用泛型接口结合协变性。以下是一个示例，展示如何实现一个支持多个类型的生产者。

协变性

using System;
using System.Collections.Generic;public interface IProducer<out T>
{T Produce();
}public class FruitProducer : IProducer<Fruit>
{public Fruit Produce(){return new Fruit("Apple");}
}public class AppleProducer : IProducer<Apple>
{public Apple Produce(){return new Apple("Granny Smith");}
}public class OrangeProducer : IProducer<Orange>
{public Orange Produce(){return new Orange("Navel Orange");}
}public class Fruit
{public string Name { get; }public Fruit(string name){Name = name;}
}public class Apple : Fruit
{public Apple(string name) : base(name) { }
}public class Orange : Fruit
{public Orange(string name) : base(name) { }
}class Program
{static void Main(){List<IProducer<Fruit>> producers = new List<IProducer<Fruit>>(){new FruitProducer(),new AppleProducer(),new OrangeProducer()};foreach (var producer in producers){ProduceFruit(producer);}}static void ProduceFruit(IProducer<Fruit> producer){Fruit fruit = producer.Produce();Console.WriteLine($"Produced: {fruit.Name}");}
}

非协变性

using System;// 定义非协变的泛型接口
public interface IProducer<T>
{T Produce();
}// 实现生产者类
public class FruitProducer : IProducer<Fruit>
{public Fruit Produce(){return new Fruit("Apple");}
}public class AppleProducer : IProducer<Apple>
{public Apple Produce(){return new Apple("Granny Smith");}
}// 基类和子类
public class Fruit
{public string Name { get; }public Fruit(string name){Name = name;}
}public class Apple : Fruit
{public Apple(string name) : base(name) { }
}// 主程序
class Program
{static void Main(){// 创建生产者实例IProducer<Fruit> fruitProducer = new FruitProducer();IProducer<Apple> appleProducer = new AppleProducer();// 生成水果和苹果Fruit fruit = fruitProducer.Produce();Apple apple = appleProducer.Produce();// 输出结果Console.WriteLine($"Produced: {fruit.Name}");Console.WriteLine($"Produced: {apple.Name}");}
}

协变性+委托

using System;// 定义协变的泛型委托
public delegate T ProducerDelegate<out T>();// 定义协变的泛型接口
public interface IProducer<out T>
{T Produce();
}// 实现生产者类
public class FruitProducer : IProducer<Fruit>
{public Fruit Produce(){return new Fruit("Apple");}
}public class AppleProducer : IProducer<Apple>
{public Apple Produce(){return new Apple("Granny Smith");}
}// 基类和子类
public class Fruit
{public string Name { get; }public Fruit(string name){Name = name;}
}public class Apple : Fruit
{public Apple(string name) : base(name) { }
}// 主程序
class Program
{static void Main(){// 创建生产者实例IProducer<Fruit> fruitProducer = new FruitProducer();IProducer<Apple> appleProducer = new AppleProducer();// 创建委托实例ProducerDelegate<Fruit> fruitDelegate = fruitProducer.Produce;ProducerDelegate<Apple> appleDelegate = appleProducer.Produce;// 生成水果和苹果Fruit fruit = fruitDelegate();Apple apple = appleDelegate();// 输出结果Console.WriteLine($"Produced: {fruit.Name}");Console.WriteLine($"Produced: {apple.Name}");}
}

非协变性+委托

using System;// 定义非协变的泛型委托
public delegate T ProducerDelegate<T>();// 定义非协变的泛型接口
public interface IProducer<T>
{T Produce();
}// 实现生产者类
public class FruitProducer : IProducer<Fruit>
{public Fruit Produce(){return new Fruit("Apple");}
}public class AppleProducer : IProducer<Apple>
{public Apple Produce(){return new Apple("Granny Smith");}
}// 基类和子类
public class Fruit
{public string Name { get; }public Fruit(string name){Name = name;}
}public class Apple : Fruit
{public Apple(string name) : base(name) { }
}// 主程序
class Program
{static void Main(){// 创建生产者实例IProducer<Fruit> fruitProducer = new FruitProducer();IProducer<Apple> appleProducer = new AppleProducer();// 创建委托实例ProducerDelegate<Fruit> fruitDelegate = fruitProducer.Produce;ProducerDelegate<Apple> appleDelegate = appleProducer.Produce;// 生成水果和苹果Fruit fruit = fruitDelegate();Apple apple = appleDelegate();// 输出结果Console.WriteLine($"Produced: {fruit.Name}");Console.WriteLine($"Produced: {apple.Name}");}
}