Why can the static class Tuple in .NET Framework 4.0 have new keyword to create instances?

Question

Static Classes and Static Class Members

In this link Microsoft says,

a static class cannot be instantiated. In other words, you cannot use the new keyword to create a variable of the class type. Because there is no instance variable, you access the members of a static class by using the class name itself.

I learned static class the same as stated above. But for the static class Tuple introduced in .NET Framework 4 can have new keyword to create a Tuple.

var population = new Tuple( "New York", 7891957, 7781984, 7894862, 7071639, 7322564, 8008278);

Another example

Can anyone explain how is that possible?

Answer 1

The static Tuple class is a factory class: it's job is just to provide an easy to way to construct tuples.

In reality, there are 8 tuple classes in .NET 4:

• 7 Generic tuples you can create instances of, with up to 8 generic argument: Tuple<T1, T2>, Tuple<T1, T2, T3> and so on.
• The static Tuple factory class which centralizes construction of the above.

So, you can't create an instance of a static class, but you can have several classes with the same name, if they have different generic arguments.