These are intended for efficient sorted insertion/deletion of a SLLNode and DLLNode. Coupled with a hash to the node itself, deletion and search can be O(1) operations, while insertion is O(1) for a prespecified location, and at worst O(n) for sorted insertion.
Note: push! isn't defined for SinglyLinkedList to reiterate that inserting at the end of the list is O(n), and in this case DoublyLinkedList should be used instead, which is more flexible at the cost of a slight increase in memory usage and complexity.
CircularBuffer is just a ring buffer with parametric type with idiomatic push! and iteration. RollingWindow sits on top of Circular buffer to retain lags of a time series. Create with a fixed IntIterable, which is a range or vector of Ints. Extract lagged values into a Vector{T} using toarray(window).