C# – Generics – What is typeof(T) ?

Answer:
typeof(T).ToString() shows name of the passed class type, however,
typeof(T) is System.RuntimeType.

This is another caveat of C# generics.

For example. Suppose you invoke this method:

    Form frm = _factoryView.CreateForm<Form>();

And the CreateForm method has following signature

    public T CreateForm<T>() where T : Form, new()

You may think this line gives you a true statement. It is not.
This line will always give a false result.

    if (typeof(T) is System.Windows.Forms.Form)

Here is complete snippet of the method.

public T CreateForm<T>() where T : Form, new()

{

    if (typeof(T) is System.Windows.Forms.Form)

        //this will always be FALSE

    T frm = new T();

    if (frm is System.Windows.Forms.Form)

        //this will be checked

}

And here is what Immediate Window shows us:

?typeof(T).ToString()
"System.Windows.Forms.Form"
?typeof(T) is System.Windows.Forms.Form
false
?typeof(T) == System.Windows.Forms.Form
'System.Windows.Forms.Form' is a 'type', which is not valid in the given context
?typeof(T) is System.RuntimeType
true
?frm is System.Windows.Forms.Form
true

Moral of the story, only apply is operator on instantiated object, never on typeof(T).