Enchanced random access support for queues

Now queues support indexing, front() and back() operations and pairs iteration.
Also modernized some of the code to use newer Nim features.
Added the "add()" alias to "enqueue()", per nim's conventions (also fits better with pop())

lib/pure/collections/queues.nim

@@ -11,6 +11,22 @@
 ## Note: For inter thread communication use
 ## a `Channel <channels.html>`_ instead.
 
+proc englishOrdinal(n: SomeInteger): string =
+  # Temporary proc. Needs to be moved somewhere else as it can be reused in
+  # other places too.
+  # If this accepted number strings instead and only gave out the letters it
+  # would be more flexible, permitting things like 1.100.000th, 34,545,321st
+  # but it would be harder and more error prone to use.
+  let num = $n
+  if num.len > 1 and num[^2] == '1':
+    return num & "th"
+  else:
+    case num[^1]
+    of '1': return num & "st"
+    of '2': return num & "nd"
+    of '3': return num & "rd"
+    else: return num & "th"
+
 import math
 
 type
@@ -20,44 +36,103 @@ type
 
 {.deprecated: [TQueue: Queue].}
 
-proc initQueue*[T](initialSize=4): Queue[T] =
+proc initQueue*[T](initialSize: int = 4): Queue[T] =
   ## creates a new queue. `initialSize` needs to be a power of 2.
   assert isPowerOfTwo(initialSize)
   result.mask = initialSize-1
   newSeq(result.data, initialSize)
 
-proc len*[T](q: Queue[T]): int =
+proc len*[T](q: Queue[T]): int {.inline.}=
   ## returns the number of elements of `q`.
   result = q.count
 
+proc low*[T](q: Queue[T]): int {.inline.}=
+  ## returns the index of the oldest element of `q` (always 0).
+  result = 0
+
+proc high*[T](q: Queue[T]): int {.inline.}=
+  ## returns the index of the last element inserted on `q` (equivalent to
+  ## `q.len - 1`).
+  result = q.count - 1
+
+proc front*[T](q: Queue[T]): T {.inline.}=
+  ## returns the oldest element of `q`. Equivalent to `q.pop()` but does not
+  ## remove it from the queue.
+  assert q.count > 0
+  result = q.data[q.rd]
+
+proc back*[T](q: Queue[T]): T {.inline.} =
+  ## returns the newest element of `q` but does not remove it from the queue.
+  assert q.count > 0
+  result = q.data[q.wr - 1]
+
+template xBoundsCheck(q, i) =
+  # Bounds check for the array like acceses.
+  when compileOption("boundChecks"):  # d:release should disable this.
+    if i > q.high:  # x < q.low is taken care by the Natural parameter
+      raise newException(IndexError,
+                         "You tried to access the " & englishOrdinal(i+1) &
+                         " element of the queue but it has only " &
+                         $q.len &  " elements.")
+  discard
+
+proc `[]`*[T](q: Queue[T], i: Natural) : T {.inline.} =
+  ## Acess the i-th element of `q` by order of insertion.
+  ## q[0] is the oldest (the next one q.pop() will extract),
+  ## q[^1] is the newest (last one added to the queue).
+  xBoundsCheck(q, i)
+  return q.data[q.rd + i and q.mask]
+
+proc `[]`*[T](q: var Queue[T], i: Natural): var T {.inline.} =
+  ## Acess the i-th element of `q` and returns a mutable
+  ## reference to it.
+  xBoundsCheck(q, i)
+  return q.data[q.rd + i and q.mask]
+
+proc `[]=`* [T] (q: var Queue[T], i: Natural, val : T) {.inline.} =
+  ## Change the i-th element of `q`.
+  xBoundsCheck(q, i)
+  q.data[q.rd + i and q.mask] = val
+
 iterator items*[T](q: Queue[T]): T =
   ## yields every element of `q`.
   var i = q.rd
-  var c = q.count
-  while c > 0:
-    dec c
+  for c in 0 ..< q.count:
     yield q.data[i]
     i = (i + 1) and q.mask
 
 iterator mitems*[T](q: var Queue[T]): var T =
   ## yields every element of `q`.
   var i = q.rd
-  var c = q.count
-  while c > 0:
-    dec c
+  for c in 0 ..< q.count:
     yield q.data[i]
     i = (i + 1) and q.mask
 
+iterator pairs*[T](q: Queue[T]): tuple[key: int, val: T] =
+  ## yields every (position, value) of `q`.
+  var i = q.rd
+  for c in 0 ..< q.count:
+    yield (c, q.data[i])
+    i = (i + 1) and q.mask
+
+proc contains*[T](q: Queue[T], item: T): bool {.inline.} =
+  ## Returns true if `item` is in `q` or false if not found. Usually used
+  ## via the ``in`` operator. It is the equivalent of ``q.find(item) >= 0``.
+  ##
+  ## .. code-block:: Nim
+  ##   if x in q:
+  ##     assert q.contains x
+  for e in q:
+    if e == item: return true
+  return false
+
 proc add*[T](q: var Queue[T], item: T) =
   ## adds an `item` to the end of the queue `q`.
   var cap = q.mask+1
   if q.count >= cap:
-    var n: seq[T]
-    newSeq(n, cap*2)
-    var i = 0
-    for x in items(q):
-      shallowCopy(n[i], x)
-      inc i
+    var n {.noinit.} = newSeq[T](cap*2)
+    for i, x in q:
+      shallowCopy(n[i], x)  # does not use copyMem because the GC.
     shallowCopy(q.data, n)
     q.mask = cap*2 - 1
     q.wr = q.count
@@ -66,21 +141,25 @@ proc add*[T](q: var Queue[T], item: T) =
   q.data[q.wr] = item
   q.wr = (q.wr + 1) and q.mask
 
-proc enqueue*[T](q: var Queue[T], item: T) =
-  ## alias for the ``add`` operation.
-  add(q, item)
-
-proc dequeue*[T](q: var Queue[T]): T =
-  ## removes and returns the first element of the queue `q`.
+proc pop*[T](q: var Queue[T]): T =
+  ## removes and returns the first (oldest) element of the queue `q`.
   assert q.count > 0
   dec q.count
   result = q.data[q.rd]
   q.rd = (q.rd + 1) and q.mask
 
+proc enqueue*[T](q: var Queue[T], item: T) =
+  ## alias for the ``add`` operation.
+  q.add(item)
+
+proc dequeue*[T](q: var Queue[T]): T =
+  ## alias for the ``pop`` operation.
+  q.pop()
+
 proc `$`*[T](q: Queue[T]): string =
   ## turns a queue into its string representation.
   result = "["
-  for x in items(q):
+  for x in q:
     if result.len > 1: result.add(", ")
     result.add($x)
   result.add("]")
@@ -89,14 +168,37 @@ when isMainModule:
   var q = initQueue[int]()
   q.add(123)
   q.add(9)
-  q.add(4)
-  var first = q.dequeue
+  q.enqueue(4)
+  var first = q.dequeue()
   q.add(56)
   q.add(6)
-  var second = q.dequeue
+  var second = q.pop()
   q.add(789)
 
   assert first == 123
   assert second == 9
   assert($q == "[4, 56, 6, 789]")
 
+  assert q[0] == q.front and q.front == 4
+  assert q[^1] == q.back and q.back == 789
+  q[0] = 42
+  q[^1] = 7
+  assert q[q.low] == 42
+  assert q[q.high] == 7
+
+  assert 6 in q and 789 notin q
+  assert q.find(6) >= 0
+  assert q.find(789) < 0
+
+  for i in -2 .. 10:
+    if i in q:
+      assert q.contains(i) and q.find(i) >= 0
+    else:
+      assert(not q.contains(i) and q.find(i) < 0)
+
+  when compileOption("boundChecks"):
+    try:
+      echo q[99]
+      assert false
+    except IndexError:
+      discard