What is the difference between a generic method limited by inheritance and a base class parameter?

Question

Suppose I have the following code:

public class BaseClass { }
public class DerivedClass : BaseClass { }

public void GenericMethod<T>(T input) where T : BaseClass
{
 //code
}

public void NormalMethod(BaseClass input)
{
 //code
}

My question is what is the difference between the two methods? Is there any advantages or disadvantages to either method, and why?

In that particular scenario there really isn't any point in using a generic. Using the base class would be fine. Though there could be something in `code` that would warrant this — Liam, May 30 '18 at 10:21
There is no difference in this case, you have found a perfect way to do the same things 2 different ways — TheGeneral, May 30 '18 at 10:21
Possible duplicate of [What is cool about generics, why use them?](https://stackoverflow.com/questions/77632/what-is-cool-about-generics-why-use-them) — Liam, May 30 '18 at 10:22
Contrast them with methods in a fluent API where the methods *return their input* after their action. Consider what the return types are then and what that means for fluent APIs. — Damien_The_Unbeliever, May 30 '18 at 10:22
Also [When is it Appropriate to use Generics Versus Inheritance?](https://stackoverflow.com/questions/799369/when-is-it-appropriate-to-use-generics-versus-inheritance) — Liam, May 30 '18 at 10:23

score 4 · Accepted Answer · answered May 30 '18 at 10:23

What is the difference between the two methods?

Basically none.

Is there any advantages or disadvantages to either method?

At best there is a slight (compile-time) performance improvement when you use the non-generic version, since that doesn't need a specific version of the method to be compiled. Otherwise, there is nothing significant I can think of.

What could be a use case for using generics here:

When you would return T;
When T needs to derive from a class and an interface;
If your class uses a type argument, you could follow that over specifying the required type again.

Thank you, i guess this is also a byproduct of adding generics. — Dan Horton, May 30 '18 at 10:42

score 1 · Answer 2 · answered May 30 '18 at 10:25

It makes little sense to use generics in the code you show.

On the other hand, if you were to return T as opposed to BaseClass from that method, the caller can access T-specific members instead of only members declared on BaseClass (unless they cast the return value).

What is the difference between a generic method limited by inheritance and a base class parameter?

2 Answers2