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 IndexDefect on such access. This should not be relied upon, as -d:danger or --checks:off 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(IndexDefect, 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:

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]

Creates 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.

See also:

  Source Edit 
proc toDeque[T](x: openArray[T]): Deque[T]

Creates a new deque that contains the elements of x (in the same order).

See also:

Example:

var a = toDeque([7, 8, 9])
assert len(a) == 3
assert a.popFirst == 7
assert len(a) == 2
  Source Edit 
proc len[T](deq: Deque[T]): int {...}{.inline.}
Returns the number of elements of deq.   Source Edit 
proc `[]`[T](deq: Deque[T]; i: Natural): T {...}{.inline.}
Accesses the i-th element of deq.

Example:

var a = initDeque[int]()
for i in 1 .. 5:
  a.addLast(10*i)
assert a[0] == 10
assert a[3] == 40
doAssertRaises(IndexDefect, echo a[8])
  Source Edit 
proc `[]`[T](deq: var Deque[T]; i: Natural): var T {...}{.inline.}
Accesses the i-th element of deq and return a mutable reference to it.

Example:

var a = initDeque[int]()
for i in 1 .. 5:
  a.addLast(10*i)
assert a[0] == 10
assert a[3] == 40
doAssertRaises(IndexDefect, echo a[8])
  Source Edit 
proc `[]=`[T](deq: var Deque[T]; i: Natural; val: T) {...}{.inline.}
Changes the i-th element of deq.

Example:

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.}

Accesses the backwards indexed i-th element.

deq[^1] is the last element.

Example:

var a = initDeque[int]()
for i in 1 .. 5:
  a.addLast(10*i)
assert a[^1] == 50
assert a[^4] == 20
doAssertRaises(IndexDefect, echo a[^9])
  Source Edit 
proc `[]`[T](deq: var Deque[T]; i: BackwardsIndex): var T {...}{.inline.}

Accesses the backwards indexed i-th element.

deq[^1] is the last element.

Example:

var a = initDeque[int]()
for i in 1 .. 5:
  a.addLast(10*i)
assert a[^1] == 50
assert a[^4] == 20
doAssertRaises(IndexDefect, echo a[^9])
  Source Edit 
proc `[]=`[T](deq: var Deque[T]; i: BackwardsIndex; x: T) {...}{.inline.}

Changes the backwards indexed i-th element.

deq[^1] is the last element.

Example:

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.}

Returns 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)

Adds an item to the beginning of the deq.

See also:

Example:

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)

Adds an item to the end of the deq.

See also:

Example:

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:

Example:

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:

Example:

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

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

See also:

Example:

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: var Deque[T]): var T {...}{.inline.}

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

See also:

Example:

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.}

Removes and returns the first element of the deq.

See also:

Example:

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.}

Removes and returns the last element of the deq.

See also:

Example:

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:

Example:

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)

Removes 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:

Example:

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
Turns a deque into its string representation.   Source Edit

Iterators

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

Yields 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
Yields every element of deq, which can be modified.

Example:

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]

Yields 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

Made with Nim. Generated: 2021-05-25 07:36:14 UTC