返回派生类的泛型方法引发对象必须实现IConvertible异常

Question

I have a base class:

public class TestBase
{
}

I have a derived class

public class TestDerived: TestBase
{
}

I have a generic method

  public class SomeClass
  {
   public T GetInstance()
   {
      var inst=new TestDerived();
      return (T)Convert.ChangeType(inst, typeof(T)); //exception thrown here
   }
  }

I make a call:

    SomeClass test=new SomeClass()
    var x= test.GetInstance<TestBase>(); 

Why do I get an exception saying System.InvalidCastException : Object must implement IConvertible.

Answer 1

By using constraints you can let the compiler know T is based off TestBase. This way you get to avoid losing type checking.

public class SomeClass
{
   public T GetInstance() where T : TestBase
   {
      var inst=new TestDerived();
      return inst;
   }
}

But why do you need to use generics at all? There's nothing here that benefits from it.