C# 在实例化后更改通用对象？

Question

是否可以在实例化 SomeClass 后将 TEntity 更改为 NewEntity？

例如，拿这个类定义:

public class SomeClass<TEntity> where TEntity : class
{
   public void ChangeSet<NewEntity>()
    {
        TEntity = NewEntity;//not valid
    }
 }

例如像这样实例化:

var sc = new SomeClass<SomeEntity>();

我怎样才能做到这一点？

sc.ChangeSet<NewEntity>();

Answer 1

Is it possible to change TEntity to NewEntity after SomeClass has been instantiated?

不，这是不可能的。 CLR 如何知道如何将值从 TEntity 映射到 SomeEntity？它们是不同的类型。这就像要求您的杂货商将苹果变成橙子一样。

下面的代码不推荐。您需要担心的问题太多了，而且很容易出现错误。我提供它作为您要求 CLR 执行的操作的示例。

SomeClass<Foo> fooClass = new SomeClass<Foo>():
//do stuff to fooClass
SomeClass<Baz> = fooClass.ChangeSet<Baz>();

public class SomeClass<T> where T : class
{
    public SomeClass<K> ChangeSet<K>() where K:class
    {
       var changed = new SomeClass<K>();
       //manually map the properties over
       //but how do you know that Foo.PropertyA fits into Baz.PropetyZed?
       //what happens if Foo.A has a string length of 100, but Baz.A has a max length of 50? What do you do?
       //What id Foo.ID is an INT and Baz.ID is a GUID?
       return changed;
    }
}