.NET Collection that is a struct

Here's an interesting question ... is there a collection that is a struct somewhere in the .net framework?

Just to clarify, all of the existing collections (List, array, etc.) are all reference types ... even if you set the generic parameter to a value type. But I want to know if there's a way I can make a collection that is actually a struct. I obviously wouldn't plan on passing this around (which would result in a ton of copying) ... I'd keep it as a private member in my class (internal state) so it's only defined once. The idea is that I would be able to avoid invoking the garbage collector just to make a small collection (think XNA).

Assuming one does not exist, a secondary part of the question is, what would be the ideal data structure for this. linked list?

Solution

No, such a type does not exist and it would not be a good idea. Structs should be small immutable value types according to the Microsoft guidelines.

From the Value Type Usage Guidelines:

Act like primitive types.

Have an instance size under 16 bytes.

Are immutable.

Value semantics are desirable.

It would be difficult to implement a linked list as a value type because linked lists are typically defined recursively. This works fine:

class Node<T>
{
    public T Value;
    public Node<T> Next;
}

But this fails because structs have a fixed size and that size must be known when the struct is defined:

struct Node<T>
{
    public T Value;

    // Error: Struct member 'Node<T>.Next' of type 'Node<T>'
    // causes a cycle in the struct layout
    public Node<T> Next; 
}