/**
 * A deque, for fun.  Untested as of yet.  Likely buggy.
 */
type t[T] =
    obj {
        fn size() -> uint ;
        fn add_front(&T) ;
        fn add_back(&T) ;
        fn pop_front() -> T ;
        fn pop_back() -> T ;
        fn peek_front() -> T ;
        fn peek_back() -> T ;
        fn get(int) -> T ;
    };

fn create[@T]() -> t[T] {
    type cell[T] = option::t[T];

    let initial_capacity: uint = 32u; // 2^5
     /**
      * Grow is only called on full elts, so nelts is also len(elts), unlike
      * elsewhere.
      */


    fn grow[@T](nelts: uint, lo: uint, elts: &(cell[T])[mutable ]) ->
       (cell[T])[mutable ] {
        assert (nelts == ivec::len(elts));
        let rv = ~[mutable ];

        let i = 0u;
        let nalloc = uint::next_power_of_two(nelts + 1u);
        while i < nalloc {
            if i < nelts {
                rv += ~[mutable elts.((lo + i) % nelts)];
            } else { rv += ~[mutable option::none]; }
            i += 1u;
        }

        ret rv;
    }
    fn get[@T](elts: &(cell[T])[mutable ], i: uint) -> T {
        ret alt elts.(i) { option::some(t) { t } _ { fail } };
    }
    obj deque[@T](mutable nelts: uint,
                  mutable lo: uint,
                  mutable hi: uint,
                  mutable elts: (cell[T])[mutable ]) {
        fn size() -> uint { ret nelts; }
        fn add_front(t: &T) {
            let oldlo: uint = lo;
            if lo == 0u {
                lo = ivec::len[cell[T]](elts) - 1u;
            } else { lo -= 1u; }
            if lo == hi {
                elts = grow[T](nelts, oldlo, elts);
                lo = ivec::len[cell[T]](elts) - 1u;
                hi = nelts;
            }
            elts.(lo) = option::some[T](t);
            nelts += 1u;
        }
        fn add_back(t: &T) {
            if lo == hi && nelts != 0u {
                elts = grow[T](nelts, lo, elts);
                lo = 0u;
                hi = nelts;
            }
            elts.(hi) = option::some[T](t);
            hi = (hi + 1u) % ivec::len[cell[T]](elts);
            nelts += 1u;
        }

        /**
         * We actually release (turn to none()) the T we're popping so
         * that we don't keep anyone's refcount up unexpectedly.
         */
        fn pop_front() -> T {
            let t: T = get[T](elts, lo);
            elts.(lo) = option::none[T];
            lo = (lo + 1u) % ivec::len[cell[T]](elts);
            nelts -= 1u;
            ret t;
        }
        fn pop_back() -> T {
            if hi == 0u {
                hi = ivec::len[cell[T]](elts) - 1u;
            } else { hi -= 1u; }
            let t: T = get[T](elts, hi);
            elts.(hi) = option::none[T];
            nelts -= 1u;
            ret t;
        }
        fn peek_front() -> T { ret get[T](elts, lo); }
        fn peek_back() -> T { ret get[T](elts, hi - 1u); }
        fn get(i: int) -> T {
            let idx: uint = (lo + (i as uint)) % ivec::len[cell[T]](elts);
            ret get[T](elts, idx);
        }
    }
    let v: (cell[T])[mutable ] =
        ivec::init_elt_mut(option::none, initial_capacity);
    ret deque[T](0u, 0u, 0u, v);
}
// Local Variables:
// mode: rust;
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End: