Question

Let’s say we’ve got a generic list like this:

List<string> list = new List<string>() { "abc", "demo", "stackoverflow" };

When trying to create a new instance of a stack like this, it won’t work.

Stack<string> stack = new Stack<string>() { "abc", "demo", "stackoverflow" };

The compiler says that the Stack<> doesn’t have an add method. So I implemented an add method by using the extensionmethods:

public static void Add<T>(this Stack<T> stack, T item)
{
    stack.Push(item);
}

However, the compiler still gives the same error. But why? Shouldn’t the compiler find the method now? Moreover, doesn’t the generic stack implement IEnumerable<> and ICollection<>? Why doesn’t the stack contain the Add method by default?

Answer 1

Collection initializers do not use extension methods; as such, you cannot use a collection initializer with something that does not have an Add method-group, such as Stack<T>. You could perhaps subclass it, but please don’t:

class MyStack<T> : Stack<T> // yeuch
{
    public void Add(T item)
    {
        Push(item);
    }
}
...
// please don't do this... think of the kittens...
Stack<string> stack = new MyStack<string>() { "abc", "demo", "stackoverflow" };