Deque

Construct with an element schema in front of the module name, for example Int32 Deque.

Fields

• CONTAINER: container marker field.
• DEQUE: deque marker field.
• elementType: Ref to the element schema.
• head: front-side backing array.
• tail: back-side backing array.

Public methods

• iter (-- iter): iterates stored items in logical deque order.
• size (-- count): returns the current item count.
• pushBack (item --): appends one item at the back.
• pushFront (item --): prepends one item at the front.
• popBack (--): removes the last item.
• popFront (--): removes the first item.
• back (-- ref): returns Ref to the last item.
• front (-- ref): returns Ref to the first item.
• at (ordinal -- ref): returns Ref to the item at the zero-based ordinal.
• clear (--): removes all items while preserving the backing-array capacities.
• release (--): releases both backing arrays.

Internal helper

• swapBuffers (from to --): moves half-buffer contents during internal rebalancing when one side becomes empty.

Order and returned references

• The logical front is formed by the end of head; the logical back is formed by the end of tail.
• at 0 returns the same item as front.
• at (size 1 -) returns the same item as back.
• iter traverses items in logical deque order, not in the physical order of head or tail.
• front, back, and at return references into the current backing arrays.
• Operations that modify, rebalance, clear, or release those backing arrays may invalidate earlier returned references.

Invalid operations

• front, back, popFront, and popBack require one non-empty deque.
• at requires one ordinal in the range 0 .. size 1 -.

Examples

Runtime example: front, back, and ordinal access

"Deque" use
"String" use
"control" use

{} Int32 {} [
  d: Int32 Deque;
  10 @d.pushBack
  20 @d.pushFront
  30 @d.pushBack
  ("front=" @d.front new LF
   "back=" @d.back new LF
   "at1=" 1 @d.at new LF) printList
  @d.popFront
  ("size=" d.size LF
   "front2=" @d.front new LF) printList
  0
] "main" exportFunction

Expected Output

front=20
back=30
at1=10
size=2
front2=10

Runtime example: iteration order

"Deque" use
"String" use
"control" use

{} Int32 {} [
  d: Int32 Deque;
  10 @d.pushBack
  20 @d.pushFront
  30 @d.pushBack
  it: @d.iter;
  item0: ok0: @it.next;;
  item1: ok1: @it.next;;
  item2: ok2: @it.next;;
  item3: ok3: @it.next;;
  ("ok0=" ok0 LF
   "v0=" item0 new LF
   "ok1=" ok1 LF
   "v1=" item1 new LF
   "ok2=" ok2 LF
   "v2=" item2 new LF
   "ok3=" ok3 LF) printList
  0
] "main" exportFunction

Expected Output

ok0=TRUE
v0=20
ok1=TRUE
v1=10
ok2=TRUE
v2=30
ok3=FALSE

See also

• Array: Growable array.
• PriorityQueue: Priority queue with customizable comparison.
• algorithm: Collection interfaces, comparison helpers, iteration adapters, and view slicing utilities.