example4.cs

[CollectionBuilder(typeof(ImmutableStackBuilder), nameof(ImmutableStackBuilder.Create))]
public class ImmutableStack<T>
{
    private readonly ImmutableList<T> _items;
   
   internal ImmutableStack(){}
   
    internal ImmutableStack(ImmutableList<T> items)
    {
        _items = items;
    }
    
    public T Peek() => _items[^1];
    public ImmutableStack<T> Push(T item) => new(_items.Add(item));
    public ImmutableStack<T> Pop() => new(_items.RemoveAt(_items.Count - 1));
	
	 public IEnumerator<T> GetEnumerator() => _items.GetEnumerator();
}

public static class ImmutableStackBuilder
{
    public static ImmutableStack<T> Create<T>(ReadOnlySpan<T> items)
    {
        return new ImmutableStack<T>(ImmutableList.Create<T>(items));
    }
}