Question

to avoid confusion I summarised some code:

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            IManager<ISpecificEntity> specificManager = new SpecificEntityManager();
            IManager<IIdentifier> manager = (IManager<IIdentifier>) specificManager;
            manager.DoStuffWith(new SpecificEntity());
        }
    }

    internal interface IIdentifier
    {
    }

    internal interface ISpecificEntity : IIdentifier
    {
    }

    internal class SpecificEntity : ISpecificEntity
    {
    }

    internal interface IManager<TIdentifier> where TIdentifier : IIdentifier
    {
        void DoStuffWith(TIdentifier entity);
    }

    internal class SpecificEntityManager : IManager<ISpecificEntity>
    {
        public void DoStuffWith(ISpecificEntity specificEntity)
        {
        }
    }
}

当我对代码进行抽打时,I在<代码>Main()上获得了英瓦利德CastException。

I know that ISpecificEntity implements IIdentifier. But obviously a direct cast from an IManager<ISpecificEntity> into an IManager<IIdentifier> does not work.

我认为,与共体合作可做trick,但可修改<条码>IManager<TIdentifier> into IManager<in TIdentifier>。

因此,有没有办法将<条码>具体编码>Manager输入<条码>IManager<IIdentifier>?

感谢一切最好。

Answer 1

有了IManager<IIdentifier>,你可以做:

IIdentifier entity = new NotSpecificEntity();
manager.DoStuffWith(entity);

这将导致在您的<代码>中出现例外情形,因为它仅接受类型的<代码> 特定性参数。

UPDATE: You can read more about covariance and contravariance in C# at Eric Lippert s blog

Answer 2

为什么不:

ISpecificEntity bankAccountManager = new SpecificEntity();
IManager<IIdentifier> manager = (IManager<IIdentifier>)bankAccountManager;
manager.DoStuffWith(new SpecificEntity());

?

友情链接