Difference between a base class and a contitioned generic

Question

I noticed after some time using generics that there was not much difference between this:

public void DoSomething<T>(T t) where T : BaseClass{

}

and this:

public void DoSomething(BaseClass t){

}

The only difference I have seen so far is that the first method could be added other constraints, like interfaces or new (), but if you use it just the way that I wrote it, I don´t see much difference. Can anybody point any important factors about choosing one or another?

Answer 1

I think most visible difference is type of the parameter inside method will be different - in generic case actual type, non-generic - always BaseClass.

This information is useful when you need to call other generic classes/methods.

 class Cat : Animal {}

 void DoSomething<T>(T animal) where T:Animal
 {
    IEnumerable<T> repeatGeneric = Enumerable.Repeat(animal, 3);
    var repeatGenericVar = Enumerable.Repeat(animal, 3);
 } 
 void DoSomething(Animal animal)
 {
    IEnumerable<Animal> repeat = Enumerable.Repeat(animal, 3);
    var repeatVar = Enumerable.Repeat(animal, 3);
 } 

Now if you call both with new Cat():

• type of both repeatGeneric and repeatGenericVar will be IEnumerable<Cat> (note that var statically finds the type, shown to highlight the fact type is known statically)
• type of both repeat and repeatVar will be IEnumrable<Animal> despite the fact that Cat was passed in.