default(T) versus Activator.CreateInstance(T)

Question

I would like to know if the below statements ever return a different result for reference types, or are they identical?

1. default(T)
2. Activator.CreateInstance(T)

If they are identical, could you always use default(T), in this example, if the aim was to output the default value of T?:

if (typeof(T).IsValueType || typeof(T) == typeof(String))
{
     return default(T);
}
else
{
     return Activator.CreateInstance<T>();
}

Best way to test if a generic type is a string? (c#)

ta!

Answer 1

For reference types, default(T) will be null, whereas the CreateInstance actually returns a new object of type T (or fails if there is no suitable constructor), so the result will never be identical.

Answer 2

They are entirely different.

1. default(T), when T is a reference type, will always be null.
2. Activator.CreateInstance<T>() will create a new instance of that type using the default constructor if present, otherwise, throws MissingMethodException.