C# create Object obj = new T()? [duplicate]

Question

I have a superclass we can call class A and few subclasses, e.g. class a1 : A, class a2 : A, ... and a6 : A. In my class B, I have a set of methods that creates and adds one of the subclasses to a List<A>in B.

I want to shorten my code I have at the moment. So instead of writing

Adda1()
{
    aList.Add( new a1() );
}

Adda2()
{
    aList.Add( new a2() );
} 

...

Adda6()
{
    aList.Add( new a6() );
}

Instead I want to write something similar to this

Add<T>()
{
    aList.Add( new T() );  // This gives an error saying there is no class T.
}

Is that possible?

Is it also possible to constraint that T has to be of type A or one of its subclasses?

Answer 1

Lee's answer is correct.

The reason is that in order to be able to call new T() you need to add a new() constraint to your type parameter:

void Add<T>() where T : new()
{
     ... new T() ...
}

You also need a constraint T : A so that you can add your object of type T to a List<A>.

Note: When you use new() together with other contraints, the new() constraint must come last.

Related

• Constraints on Type Parameters

Answer 2

public void Add<T>() where T : A, new()
{
    aList.Add(new T());
}