C#泛型:简化类型签名

Question

如果我有一个如下所示的通用Item类:

abstract class Item<T>
{
}

和一个看起来像这样的项目容器:

class Container<TItem, T>
    where TItem : Item<T>
{
}

由于TItem依赖于T,是否可以简化Container的类型签名,使其只需要一个类型参数？我真正想要的是这样的:

class Container<TItem>
    where TItem : Item   // this doesn't actually work, because Item takes a type parameter
{
}

所以我可以实例化如下:

class StringItem : Item<string>
{
}

var good = new Container<StringItem>();
var bad = new Container<StringItem, string>();

当TItem是StringItem时,编译器应该能够推断T是字符串,对吧？我该如何实现这一目标？

所需用法:

class MyItem : Item<string>
{
}

Container<MyItem> container = GetContainer();
MyItem item = container.GetItem(0);
item.MyMethod();

Answer 1

我想这应该可以达到你想要的效果。显然你现在Container<string>没有这样做Container<StringItem>，但由于你没有包含使用示例，我不认为这是一个问题。

using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var myContainer = new Container<string>();

            myContainer.MyItems = new List<Item<string>>();
        }
    }

    public class Item<T> { }

    public class Container<T>
    {
        // Just some property on your container to show you can use Item<T>
        public List<Item<T>> MyItems { get; set; }
    }
}

这个修改后的版本怎么样：

using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var myContainer = new Container<StringItem>();

            myContainer.StronglyTypedItem = new StringItem();
        }
    }

    public class Item<T> { }

    public class StringItem : Item<string> { }

    // Probably a way to hide this, but can't figure it out now
    // (needs to be public because it's a base type)
    // Probably involves making a container (or 3rd class??)
    // wrap a private container, not inherit it
    public class PrivateContainer<TItem, T> where TItem : Item<T> { }

    // Public interface
    public class Container<T> : PrivateContainer<Item<T>, T>
    {
        // Just some property on your container to show you can use Item<T>
        public T StronglyTypedItem { get; set; }
    }
}