I thus decided to implement these simple, but oh so useful data structures. Sure, you could reply that ruby arrays already implement all the functionalities provided by theses data structures. True, but when you are dealing with linked lists of millions of elements, having to relocate the whole array in memory to add an element can prove to be a lenghty task. Also, finding a memory chunk big enough to hold the whole array may prove challenging. Ruby arrays grow pretty fast (~1.5x) as can be seen from the following code snippet from array.c (ruby 1.9.1p243) and can rapidly become hard to store in memory.

if (idx >= ARY_CAPA(ary)) {
    long new_capa = ARY_CAPA(ary) / 2;

    if (new_capa < ARY_DEFAULT_SIZE) {
        new_capa = ARY_DEFAULT_SIZE;
    }
    if (new_capa >= ARY_MAX_SIZE - idx) {
        new_capa = (ARY_MAX_SIZE - idx) / 2;
    }
    new_capa += idx;
    ary_resize_capa(ary, new_capa);
}

And finally, theses data structures implement functionalities that are badly supported by arrays such as deleting or adding an element in the middle of a list.

The stack and queue implementation are separated from the linked list implementation to keep them as simple as possible. The linked list implementation is more extensive and is also used to implement the sorted linked list data structure. The next data structure to be added to Batfish will probably be graphs and it should include a number of basic graph algorithms.