# deques

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Implementation of a deque (double-ended queue). The underlying implementation uses a `seq`.

None of the procs that get an individual value from the deque can be used on an empty deque. If compiled with `boundChecks` option, those procs will raise an `IndexError` on such access. This should not be relied upon, as `-d:release` will disable those checks and may return garbage or crash the program.

As such, a check to see if the deque is empty is needed before any access, unless your program logic guarantees it indirectly.

    import deques

    var a = initDeque[int]()

    doAssertRaises(IndexError, echo a[0])

    for i in 1 .. 5:
      a.addLast(10*i)
    assert $a == "[10, 20, 30, 40, 50]"

    assert a.peekFirst == 10
    assert a.peekLast == 50
    assert len(a) == 5

    assert a.popFirst == 10
    assert a.popLast == 50
    assert len(a) == 3

    a.addFirst(11)
    a.addFirst(22)
    a.addFirst(33)
    assert $a == "[33, 22, 11, 20, 30, 40]"

    a.shrink(fromFirst = 1, fromLast = 2)
    assert $a == "[22, 11, 20]"

See also:

- lists module for singly and doubly linked lists and rings
- channels module for inter-thread communication

# Imports

math, typetraits

# Types

    Deque[T] = object
      data: seq[T]
      head, tail, count, mask: int

  A double-ended queue backed with a ringed seq buffer.

  To initialize an empty deque use initDeque proc.

  Source Edit

# Procs

    proc initDeque[T](initialSize: int = 4): Deque[T]

  Create a new empty deque.

  Optionally, the initial capacity can be reserved via `initialSize` as a performance optimization. The length of a newly created deque will still be 0.

  `initialSize` must be a power of two (default: 4). If you need to accept runtime values for this you could use the nextPowerOfTwo proc from the math module.

  Source Edit

    proc len[T](deq: Deque[T]): int {...}{.inline.}

  Return the number of elements of `deq`. Source Edit

    proc `[]`[T](deq: Deque[T]; i: Natural): T {...}{.inline.}

  Access the i-th element of `deq`.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert a[0] == 10
      assert a[3] == 40
      doAssertRaises(IndexError, echo a[8])

  Source Edit

    proc `[]`[T](deq: var Deque[T]; i: Natural): var T {...}{.inline.}

  Access the i-th element of `deq` and return a mutable reference to it.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert a[0] == 10
      assert a[3] == 40
      doAssertRaises(IndexError, echo a[8])

  Source Edit

    proc `[]=`[T](deq: var Deque[T]; i: Natural; val: T) {...}{.inline.}

  Change the i-th element of `deq`.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      a[0] = 99
      a[3] = 66
      assert $a == "[99, 20, 30, 66, 50]"

  Source Edit

    proc `[]`[T](deq: Deque[T]; i: BackwardsIndex): T {...}{.inline.}

  Access the backwards indexed i-th element.

  `deq[^1]` is the last element.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert a[^1] == 50
      assert a[^4] == 20
      doAssertRaises(IndexError, echo a[^9])

  Source Edit

    proc `[]`[T](deq: var Deque[T]; i: BackwardsIndex): var T {...}{.inline.}

  Access the backwards indexed i-th element.

  `deq[^1]` is the last element.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert a[^1] == 50
      assert a[^4] == 20
      doAssertRaises(IndexError, echo a[^9])

  Source Edit

    proc `[]=`[T](deq: var Deque[T]; i: BackwardsIndex; x: T) {...}{.inline.}

  Change the backwards indexed i-th element.

  `deq[^1]` is the last element.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      a[^1] = 99
      a[^3] = 77
      assert $a == "[10, 20, 77, 40, 99]"

  Source Edit

    proc contains[T](deq: Deque[T]; item: T): bool {...}{.inline.}

  Return true if `item` is in `deq` or false if not found.

  Usually used via the `in` operator. It is the equivalent of `deq.find(item) >= 0`.

      if x in q:
        assert q.contains(x)

  Source Edit

    proc addFirst[T](deq: var Deque[T]; item: T)

  Add an `item` to the beginning of the `deq`.

  See also:

  - addLast proc
  - peekFirst proc
  - peekLast proc
  - popFirst proc
  - popLast proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addFirst(10 * i)
      assert $a == "[50, 40, 30, 20, 10]"

  Source Edit

    proc addLast[T](deq: var Deque[T]; item: T)

  Add an `item` to the end of the `deq`.

  See also:

  - addFirst proc
  - peekFirst proc
  - peekLast proc
  - popFirst proc
  - popLast proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert $a == "[10, 20, 30, 40, 50]"

  Source Edit

    proc peekFirst[T](deq: Deque[T]): T {...}{.inline.}

  Returns the first element of `deq`, but does not remove it from the deque.

  See also:

  - addFirst proc
  - addLast proc
  - peekLast proc
  - popFirst proc
  - popLast proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert $a == "[10, 20, 30, 40, 50]"
      assert a.peekFirst == 10
      assert len(a) == 5

  Source Edit

    proc peekLast[T](deq: Deque[T]): T {...}{.inline.}

  Returns the last element of `deq`, but does not remove it from the deque.

  See also:

  - addFirst proc
  - addLast proc
  - peekFirst proc
  - popFirst proc
  - popLast proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert $a == "[10, 20, 30, 40, 50]"
      assert a.peekLast == 50
      assert len(a) == 5

  Source Edit

    proc popFirst[T](deq: var Deque[T]): T {...}{.inline, discardable.}

  Remove and returns the first element of the `deq`.

  See also:

  - addFirst proc
  - addLast proc
  - peekFirst proc
  - peekLast proc
  - popLast proc
  - clear proc
  - shrink proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert $a == "[10, 20, 30, 40, 50]"
      assert a.popFirst == 10
      assert $a == "[20, 30, 40, 50]"

  Source Edit

    proc popLast[T](deq: var Deque[T]): T {...}{.inline, discardable.}

  Remove and returns the last element of the `deq`.

  See also:

  - addFirst proc
  - addLast proc
  - peekFirst proc
  - peekLast proc
  - popFirst proc
  - clear proc
  - shrink proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert $a == "[10, 20, 30, 40, 50]"
      assert a.popLast == 50
      assert $a == "[10, 20, 30, 40]"

  Source Edit

    proc clear[T](deq: var Deque[T]) {...}{.inline.}

  Resets the deque so that it is empty.

  See also:

  - clear proc
  - shrink proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addFirst(10 * i)
      assert $a == "[50, 40, 30, 20, 10]"
      clear(a)
      assert len(a) == 0

  Source Edit

    proc shrink[T](deq: var Deque[T]; fromFirst = 0; fromLast = 0)

  Remove `fromFirst` elements from the front of the deque and `fromLast` elements from the back.

  If the supplied number of elements exceeds the total number of elements in the deque, the deque will remain empty.

  See also:

  - clear proc

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addFirst(10 * i)
      assert $a == "[50, 40, 30, 20, 10]"
      a.shrink(fromFirst = 2, fromLast = 1)
      assert $a == "[30, 20]"

  Source Edit

    proc `$`[T](deq: Deque[T]): string

  Turn a deque into its string representation. Source Edit

# Iterators

    iterator items[T](deq: Deque[T]): T

  Yield every element of `deq`.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 3:
        a.addLast(10*i)

      for x in a:  # the same as: for x in items(a):
        echo x

      # 10
      # 20
      # 30

  Source Edit

    iterator mitems[T](deq: var Deque[T]): var T

  Yield every element of `deq`, which can be modified.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 5:
        a.addLast(10 * i)
      assert $a == "[10, 20, 30, 40, 50]"
      for x in mitems(a):
        x = 5 * x - 1
      assert $a == "[49, 99, 149, 199, 249]"

  Source Edit

    iterator pairs[T](deq: Deque[T]): tuple[key: int, val: T]

  Yield every (position, value) of `deq`.

  Examples:

      var a = initDeque[int]()
      for i in 1 .. 3:
        a.addLast(10*i)

      for k, v in pairs(a):
        echo "key: ", k, ", value: ", v

      # key: 0, value: 10
      # key: 1, value: 20
      # key: 2, value: 30

  Source Edit