Why can't you declare a static struct in C#, but they can have static methods?

Question

// OK struct MyStruct {     static void Foo() { } }  // Error static struct MyStruct { } 

Answer 1

Since you cannot create an instance of a static type, the behavior of static struct would be exactly the same as the behavior of static class. So, there is no reason for creating them. I think it would be theoretically possible to have a static struct but it would be confusing - how would you choose between static class and static struct if the behavior of the two was exactly the same?

Note that static methods inside a struct are quite useful as you can use them for operations related to the struct, for example DateTime.TryParse etc.

Technically speaking I don't think that the current C# compiler & runtime could produce something like a static struct, because internally (at the IL level) static class is a class that is marked as abstract and sealed. And I suppose that you cannot create a struct that would be abstract and sealed (in the IL).

Answer 2

I think the key, really, is that a struct is a value type, not a reference type. That would be like saying "There's only one instance of int for my entire program. It can have different values, but only one at a time." Further, whenever you pass a struct as an argument, it gets passed by value, that is, a copy of the struct is made and placed on the stack. This defeats the purpose of a static definition -- which should mean that there is only (ever) one instance of the thing being defined. If what you are trying to create is really a Singleton, a class is a much better way to handle that given that it has much better creation semantics than a struct.