Intrusive single linked list, wouldn't recommend anyone actually use it :D

ilist.d

/**
 * Intrusive single linked list, uses next pointer already present in the type
 * to avoid extra dynamic memory allocation.
*/
struct ILinkedList(T) {

    T* head_;

    void add(T* item) {

        this.add(&head_, item);

    } //add

    private void add(T** node, T* new_node) {

        new_node.next = *node;
        *node = new_node;

    } //add

    void opOpAssign(string op: "~")(T* item) {

        this.add(&head_, item);

    } //opOpAssign

    int opApply(scope int delegate(T*) dg) {

        int result = 0;

        for (auto cur = head_; cur != null; cur = cur.next) {
            result = dg(cur);
            if (result) break;
        }

        return result;

    } //opApply

    /**
     * Unlinks the head of the linked list, making the next element
     * the new head of the list. (1, 2, 3, 4) -> (2, 3, 4)
    */
    void poll() {

        if (head_) {
            head_ = head_.next;
        }

    } //poll

    T* head() {

        return head_;

    } //head

    void clear() {

        head_ = null;

    } //clear

    @property bool empty() {

        return head_ == null;

    } //empty

} //ILinkedList