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.

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.

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])

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])

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]"

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])

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])

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]"

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)

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]"

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]"

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

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

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]"

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]"

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

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]"

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

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]"

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