# class Deque(T)

- Deque(T)
- Reference
- Object

##
Overview

A Deque ("double-ended queue") is a collection of objects of type T that behaves much like an Array.

Deque has a subset of Array's API. It performs better than an `Array` when there are frequent insertions or deletions of items near the beginning or the end.

The most typical use case of a Deque is a queue: use `#push` to add items to the end of the queue and `#shift` to get and remove the item at the beginning of the queue.

This Deque is implemented with a dynamic array used as a circular buffer.

##
Included Modules

- Indexable::Mutable(T)

##
Defined in:

deque.cr
json/to_json.cr

##
Constructors

- .additive_identity : self

  Returns the additive identity of this type.

- .new(size : Int, value : T)

  Creates a new `Deque` of the given size filled with the same value in each position.

- .new(array : Array(T))

  Creates a new `Deque` that copies its items from an Array.

- .new(initial_capacity : Int)

  Creates a new empty `Deque` backed by a buffer that is initially `initial_capacity` big.

- .new(pull : JSON::PullParser)
- .new

  Creates a new empty Deque

- .new(size : Int, & : Int32 -> T)

  Creates a new `Deque` of the given size and invokes the block once for each index of the deque, assigning the block's value in that index.

- .new(pull : JSON::PullParser, &)

##
Class Method Summary

- .from_json(string_or_io, &) : Nil

##
Instance Method Summary

- #+(other : Deque(U)) forall U

  Concatenation.

- #<<(value : T)

  Alias for `#push`.

- #==(other : Deque)

  Returns `true` if it is passed a `Deque` and `equals?` returns `true` for both deques, the caller and the argument.

- #clear

  Removes all elements from `self`.

- #clone

  Returns a new `Deque` that has this deque's elements cloned.

- #concat(other : Indexable) : self

  Appends the elements of other to `self`, and returns `self`.

- #concat(other : Enumerable(T)) : self
- #delete(obj) : Bool

  Removes all items from `self` that are equal to obj.

- #delete_at(index : Int) : T

  Deletes the item that is present at the index.

- #dup

  Returns a new `Deque` that has exactly this deque's elements.

- #each(& : T -> ) : Nil

  Yields each item in this deque, from first to last.

- #insert(index : Int, value : T) : self

  Insert a new item before the item at index.

- #inspect(io : IO) : Nil

  Appends a String representation of this object which includes its class name, its object address and the values of all instance variables.

- #pop(n : Int) : Nil

  Removes the last n (at most) items in the deque.

- #pop : T

  Removes and returns the last item.

- #pop(&)

  Removes and returns the last item, if not empty, otherwise executes the given block and returns its value.

- #pop? : T | Nil

  Removes and returns the last item, if not empty, otherwise `nil`.

- #pretty_print(pp)
- #push(value : T)

  Adds an item to the end of the deque.

- #reject!(& : T -> ) : self

  Modifies `self`, deleting the elements in the collection for which the passed block is truthy.

- #reject!(pattern) : self

  Modifies `self`, deleting the elements in the collection for which `pattern === element`.

- #rotate!(n : Int = 1) : Nil

  Shifts all elements of `self` to the left n times.

- #select!(& : T -> ) : self

  Modifies `self`, keeping only the elements in the collection for which the passed block is truthy.

- #select!(pattern) : self

  Modifies `self`, keeping only the elements in the collection for which `pattern === element`.

- #shift(n : Int) : Nil

  Removes the first n (at most) items in the deque.

- #shift

  Removes and returns the first item.

- #shift(&)

  Removes and returns the first item, if not empty, otherwise executes the given block and returns its value.

- #shift?

  Removes and returns the first item, if not empty, otherwise `nil`.

- #size : Int32

  Returns the number of elements in the deque.

- #to_json(json : JSON::Builder) : Nil
- #to_s(io : IO) : Nil

  Appends a short String representation of this object which includes its class name and its object address.

- #unsafe_fetch(index : Int) : T

  Returns the element at the given index, without doing any bounds check.

- #unsafe_put(index : Int, value : T)

  Sets the element at the given index to value, without doing any bounds check.

- #unshift(value : T) : self

  Adds an item to the beginning of the deque.

### Instance methods inherited from module `Indexable::Mutable(T)`

[]=(index : Int, value : T) : T []=, fill(value : T, start : Int, count : Int) : self
fill(value : T, range : Range) : self
fill(value : T) : self
fill(start : Int, count : Int, & : Int32 -> T) : self
fill(range : Range, & : Int32 -> T) : self
fill(*, offset : Int = 0, & : Int32 -> T) : self fill, map!(& : T -> _) : self map!, map_with_index!(offset = 0, & : T, Int32 -> _) : self map_with_index!, reverse! : self reverse!, rotate!(n : Int = 1) : self rotate!, shuffle!(random : Random = Random::DEFAULT) : self shuffle!, sort! : self
sort!(&block : T, T -> U) : self forall U sort!, sort_by!(&block : T -> _) : self sort_by!, swap(index0 : Int, index1 : Int) : self swap, unsafe_put(index : Int, value : T) unsafe_put, unstable_sort! : self
unstable_sort!(&block : T, T -> U) : self forall U unstable_sort!, unstable_sort_by!(&block : T -> _) : self unstable_sort_by!, update(index : Int, & : T -> _) : T update

### Instance methods inherited from module `Indexable(T)`

[](index : Int) [], []?(index : Int) []?, bsearch(& : T -> _) bsearch, bsearch_index(& : T, Int32 -> _) bsearch_index, cartesian_product(*others : Indexable) cartesian_product, combinations(size : Int = self.size) combinations, dig(index : Int, *subindexes) dig, dig?(index : Int, *subindexes) dig?, each(& : T -> )
each
each(*, start : Int, count : Int, & : T -> )
each(*, within range : Range, & : T -> ) each, each_cartesian(*others : Indexable, &)
each_cartesian(*others : Indexable) each_cartesian, each_combination(size : Int = self.size, reuse = false, &) : Nil
each_combination(size : Int = self.size, reuse = false) each_combination, each_index(& : Int32 -> ) : Nil
each_index
each_index(*, start : Int, count : Int, &) each_index, each_permutation(size : Int = self.size, reuse = false, &) : Nil
each_permutation(size : Int = self.size, reuse = false) each_permutation, each_repeated_combination(size : Int = self.size, reuse = false, &) : Nil
each_repeated_combination(size : Int = self.size, reuse = false) each_repeated_combination, empty? : Bool empty?, equals?(other : Indexable, &) : Bool
equals?(other, &) equals?, fetch(index : Int, &)
fetch(index, default) fetch, first(&) first, hash(hasher) hash, index(object, offset : Int = 0)
index(offset : Int = 0, & : T -> ) index, index!(obj, offset : Int = 0)
index!(offset : Int = 0, & : T -> ) index!, join(separator : String | Char | Number = "") : String join, last : T
last(&) last, last? : T | Nil last?, permutations(size : Int = self.size) : Array(Array(T)) permutations, repeated_combinations(size : Int = self.size) : Array(Array(T)) repeated_combinations, reverse_each(& : T -> ) : Nil
reverse_each reverse_each, rindex(value, offset = size - 1)
rindex(offset = size - 1, & : T -> ) rindex, rindex!(value, offset = size - 1)
rindex!(offset = size - 1, & : T -> ) rindex!, sample(n : Int, random : Random = Random::DEFAULT) : Array(T)
sample(random : Random = Random::DEFAULT) sample, size size, to_a(& : T -> U) : Array(U) forall U to_a, unsafe_fetch(index : Int) unsafe_fetch, values_at(*indexes : Int) values_at

### Class methods inherited from module `Indexable(T)`

cartesian_product(indexables : Indexable(Indexable)) cartesian_product, each_cartesian(indexables : Indexable(Indexable), reuse = false, &)
each_cartesian(indexables : Indexable(Indexable), reuse = false) each_cartesian

### Instance methods inherited from module `Enumerable(T)`

accumulate(initial : U) : Array(U) forall U
accumulate : Array(T)
accumulate(initial : U, &block : U, T -> U) : Array(U) forall U
accumulate(&block : T, T -> T) : Array(T) accumulate, all?(& : T -> ) : Bool
all?(pattern) : Bool
all? : Bool all?, any?(& : T -> ) : Bool
any?(pattern) : Bool
any? : Bool any?, chunks(&block : T -> U) forall U chunks, compact_map(& : T -> _) compact_map, count(& : T -> ) : Int32
count(item) : Int32 count, cycle(n, & : T -> ) : Nil
cycle(& : T -> ) : Nil cycle, each(& : T -> ) each, each_cons(count : Int, reuse = false, &) each_cons, each_cons_pair(& : T, T -> ) : Nil each_cons_pair, each_slice(count : Int, reuse = false, &) each_slice, each_step(n : Int, *, offset : Int = 0, & : T -> ) : Nil each_step, each_with_index(offset = 0, &) each_with_index, each_with_object(obj : U, & : T, U -> ) : U forall U each_with_object, empty? : Bool empty?, find(if_none = nil, & : T -> ) find, find!(& : T -> ) : T find!, first(&)
first(count : Int) : Array(T)
first : T first, first? : T | Nil first?, flat_map(& : T -> _) flat_map, group_by(& : T -> U) forall U group_by, in_groups_of(size : Int, filled_up_with : U = nil) forall U
in_groups_of(size : Int, filled_up_with : U = nil, reuse = false, &) forall U in_groups_of, in_slices_of(size : Int) : Array(Array(T)) in_slices_of, includes?(obj) : Bool includes?, index(& : T -> ) : Int32 | Nil
index(obj) : Int32 | Nil index, index!(& : T -> ) : Int32
index!(obj) : Int32 index!, index_by(& : T -> U) : Hash(U, T) forall U index_by, join(io : IO, separator = "") : Nil
join(separator, io : IO) : Nil
join(separator = "") : String
join(io : IO, separator = "", & : T, IO -> )
join(separator, io : IO, &)
join(separator = "", & : T -> ) join, map(& : T -> U) : Array(U) forall U map, map_with_index(offset = 0, & : T, Int32 -> U) : Array(U) forall U map_with_index, max(count : Int) : Array(T)
max : T max, max? : T | Nil max?, max_by(& : T -> U) : T forall U max_by, max_by?(& : T -> U) : T | Nil forall U max_by?, max_of(& : T -> U) : U forall U max_of, max_of?(& : T -> U) : U | Nil forall U max_of?, min(count : Int) : Array(T)
min : T min, min? : T | Nil min?, min_by(& : T -> U) : T forall U min_by, min_by?(& : T -> U) : T | Nil forall U min_by?, min_of(& : T -> U) : U forall U min_of, min_of?(& : T -> U) : U | Nil forall U min_of?, minmax : Tuple(T, T) minmax, minmax? : Tuple(T | Nil, T | Nil) minmax?, minmax_by(& : T -> U) : Tuple(T, T) forall U minmax_by, minmax_by?(& : T -> U) : Tuple(T, T) | Tuple(Nil, Nil) forall U minmax_by?, minmax_of(& : T -> U) : Tuple(U, U) forall U minmax_of, minmax_of?(& : T -> U) : Tuple(U, U) | Tuple(Nil, Nil) forall U minmax_of?, none?(& : T -> ) : Bool
none?(pattern) : Bool
none? : Bool none?, one?(& : T -> ) : Bool
one?(pattern) : Bool
one? : Bool one?, partition(& : T -> ) : Tuple(Array(T), Array(T))
partition(type : U.class) forall U partition, present? : Bool present?, product(initial : Number)
product
product(initial : Number, & : T -> )
product(& : T -> _) product, reduce(memo, &)
reduce(&) reduce, reduce?(&) reduce?, reject(& : T -> )
reject(type : U.class) forall U
reject(pattern) : Array(T) reject, sample(n : Int, random : Random = Random::DEFAULT) : Array(T)
sample(random : Random = Random::DEFAULT) : T sample, select(& : T -> )
select(type : U.class) : Array(U) forall U
select(pattern) : Array(T) select, size : Int32 size, skip(count : Int) skip, skip_while(& : T -> ) : Array(T) skip_while, sum(initial)
sum
sum(initial, & : T -> )
sum(& : T -> ) sum, take_while(& : T -> ) : Array(T) take_while, tally(hash)
tally : Hash(T, Int32) tally, tally_by(hash, &)
tally_by(&block : T -> U) : Hash(U, Int32) forall U tally_by, to_a : Array(T)
to_a(& : T -> U) : Array(U) forall U to_a, to_h
to_h(& : T -> Tuple(K, V)) forall K, V to_h, to_set : Set(T)
to_set(&block : T -> U) : Set(U) forall U to_set, zip(*others : Indexable | Iterable | Iterator, &)
zip(*others : Indexable | Iterable | Iterator) zip, zip?(*others : Indexable | Iterable | Iterator, &)
zip?(*others : Indexable | Iterable | Iterator) zip?

### Class methods inherited from module `Enumerable(T)`

element_type(x) element_type

### Instance methods inherited from module `Iterable(T)`

chunk(reuse = false, &block : T -> U) forall U chunk, chunk_while(reuse : Bool | Array(T) = false, &block : T, T -> B) forall B chunk_while, cycle(n)
cycle cycle, each each, each_cons(count : Int, reuse = false) each_cons, each_cons_pair each_cons_pair, each_slice(count : Int, reuse = false) each_slice, each_step(n : Int)
each_step(n : Int, *, offset : Int) each_step, each_with_index(offset = 0) each_with_index, each_with_object(obj) each_with_object, slice_after(reuse : Bool | Array(T) = false, &block : T -> B) forall B
slice_after(pattern, reuse : Bool | Array(T) = false) slice_after, slice_before(reuse : Bool | Array(T) = false, &block : T -> B) forall B
slice_before(pattern, reuse : Bool | Array(T) = false) slice_before, slice_when(reuse : Bool | Array(T) = false, &block : T, T -> B) forall B slice_when

### Instance methods inherited from class `Reference`

==(other : self)
==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, initialize initialize, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

### Constructor methods inherited from class `Reference`

new new, unsafe_construct(address : Pointer, *args, **opts) : self unsafe_construct

### Class methods inherited from class `Reference`

pre_initialize(address : Pointer) pre_initialize

### Instance methods inherited from class `Object`

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

### Class methods inherited from class `Object`

from_json(string_or_io, root : String)
from_json(string_or_io) from_json, from_yaml(string_or_io : String | IO) from_yaml

### Macros inherited from class `Object`

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

##
Constructor Detail

def self.additive_identity : self #

Returns the additive identity of this type.

This is an empty deque.

def self.new(size : Int, value : T) #

Creates a new `Deque` of the given size filled with the same value in each position.

    Deque.new(3, 'a') # => Deque{'a', 'a', 'a'}

def self.new(array : Array(T)) #

Creates a new `Deque` that copies its items from an Array.

    Deque.new([1, 2, 3]) # => Deque{1, 2, 3}

def self.new(initial_capacity : Int) #

Creates a new empty `Deque` backed by a buffer that is initially `initial_capacity` big.

The `initial_capacity` is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If you have an estimate of the maximum number of elements a deque will hold, you should initialize it with that capacity for improved execution performance.

    deq = Deque(Int32).new(5)
    deq.size # => 0

def self.new(pull : JSON::PullParser) #
def self.new #

Creates a new empty Deque

def self.new(size : Int, & : Int32 -> T) #

Creates a new `Deque` of the given size and invokes the block once for each index of the deque, assigning the block's value in that index.

    Deque.new(3) { |i| (i + 1) ** 2 } # => Deque{1, 4, 9}

def self.new(pull : JSON::PullParser, &) #

##
Class Method Detail

def self.from_json(string_or_io, &) : Nil #

##
Instance Method Detail

def +(other : Deque(U)) forall U #

Concatenation. Returns a new `Deque` built by concatenating two deques together to create a third. The type of the new deque is the union of the types of both the other deques.

def <<(value : T) #

Alias for `#push`.

def ==(other : Deque) #

Returns `true` if it is passed a `Deque` and `equals?` returns `true` for both deques, the caller and the argument.

    deq = Deque{2, 3}
    deq.unshift 1
    deq == Deque{1, 2, 3} # => true
    deq == Deque{2, 3}    # => false

def clear #

Removes all elements from `self`.

def clone #

Returns a new `Deque` that has this deque's elements cloned. That is, it returns a deep copy of this deque.

Use `#dup` if you want a shallow copy.

def concat(other : Indexable) : self #

Appends the elements of other to `self`, and returns `self`.

    deq = Deque{"a", "b"}
    deq.concat(Deque{"c", "d"})
    deq # => Deque{"a", "b", "c", "d"}

def concat(other : Enumerable(T)) : self #
def delete(obj) : Bool #

Removes all items from `self` that are equal to obj.

    a = Deque{"a", "b", "b", "b", "c"}
    a.delete("b") # => true
    a             # => Deque{"a", "c"}

def delete_at(index : Int) : T #

Deletes the item that is present at the index. Items to the right of this one will have their indices decremented. Raises `IndexError` if trying to delete an element outside the deque's range.

    a = Deque{1, 2, 3}
    a.delete_at(1) # => 2
    a              # => Deque{1, 3}

def dup #

Returns a new `Deque` that has exactly this deque's elements. That is, it returns a shallow copy of this deque.

def each(& : T -> ) : Nil #

Yields each item in this deque, from first to last.

Do not modify the deque while using this variant of `#each`!

def insert(index : Int, value : T) : self #

Insert a new item before the item at index. Items to the right of this one will have their indices incremented.

    a = Deque{0, 1, 2}
    a.insert(1, 7) # => Deque{0, 7, 1, 2}

def inspect(io : IO) : Nil #
Description copied from class Reference

Appends a String representation of this object which includes its class name, its object address and the values of all instance variables.

    class Person
      def initialize(@name : String, @age : Int32)
      end
    end

    Person.new("John", 32).inspect # => #<Person:0x10fd31f20 @name="John", @age=32>

def pop(n : Int) : Nil #

Removes the last n (at most) items in the deque.

def pop : T #

Removes and returns the last item. Raises `IndexError` if empty.

    a = Deque{1, 2, 3}
    a.pop # => 3
    a     # => Deque{1, 2}

def pop(&) #

Removes and returns the last item, if not empty, otherwise executes the given block and returns its value.

def pop? : T | Nil #

Removes and returns the last item, if not empty, otherwise `nil`.

def pretty_print(pp) #
def push(value : T) #

Adds an item to the end of the deque.

    a = Deque{1, 2}
    a.push 3 # => Deque{1, 2, 3}

def reject!(& : T -> ) : self #

Modifies `self`, deleting the elements in the collection for which the passed block is truthy. Returns `self`.

    a = Deque{1, 6, 2, 4, 8}
    a.reject! { |x| x > 3 }
    a # => Deque{1, 2}

See also: `Deque#reject`.

def reject!(pattern) : self #

Modifies `self`, deleting the elements in the collection for which `pattern === element`.

    a = Deque{1, 6, 2, 4, 8}
    a.reject!(3..7)
    a # => Deque{1, 2, 8}

See also: `Deque#reject`.

def rotate!(n : Int = 1) : Nil #

Shifts all elements of `self` to the left n times. Returns `self`.

    a1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    a2 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    a3 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

    a1.rotate!
    a2.rotate!(1)
    a3.rotate!(3)

    a1 # => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
    a2 # => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
    a3 # => [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]

def select!(& : T -> ) : self #

Modifies `self`, keeping only the elements in the collection for which the passed block is truthy. Returns `self`.

    a = Deque{1, 6, 2, 4, 8}
    a.select! { |x| x > 3 }
    a # => Deque{6, 4, 8}

See also: `Deque#select`.

def select!(pattern) : self #

Modifies `self`, keeping only the elements in the collection for which `pattern === element`.

    ary = [1, 6, 2, 4, 8]
    ary.select!(3..7)
    ary # => [6, 4]

See also: `Deque#select`.

def shift(n : Int) : Nil #

Removes the first n (at most) items in the deque.

def shift #

Removes and returns the first item. Raises `IndexError` if empty.

    a = Deque{1, 2, 3}
    a.shift # => 1
    a       # => Deque{2, 3}

def shift(&) #

Removes and returns the first item, if not empty, otherwise executes the given block and returns its value.

def shift? #

Removes and returns the first item, if not empty, otherwise `nil`.

def size : Int32 #

Returns the number of elements in the deque.

    Deque{:foo, :bar}.size # => 2

def to_json(json : JSON::Builder) : Nil #
def to_s(io : IO) : Nil #
Description copied from class Reference

Appends a short String representation of this object which includes its class name and its object address.

    class Person
      def initialize(@name : String, @age : Int32)
      end
    end

    Person.new("John", 32).to_s # => #<Person:0x10a199f20>

def unsafe_fetch(index : Int) : T #
Description copied from module Indexable(T)

Returns the element at the given index, without doing any bounds check.

`Indexable` makes sure to invoke this method with index in `0...size`, so converting negative indices to positive ones is not needed here.

Clients never invoke this method directly. Instead, they access elements with `#[](index)` and `#[]?(index)`.

This method should only be directly invoked if you are absolutely sure the index is in bounds, to avoid a bounds check for a small boost of performance.

def unsafe_put(index : Int, value : T) #
Description copied from module Indexable::Mutable(T)

Sets the element at the given index to value, without doing any bounds check.

`Indexable::Mutable` makes sure to invoke this method with index in `0...size`, so converting negative indices to positive ones is not needed here.

Clients never invoke this method directly. Instead, they modify elements with `#[]=(index, value)`.

This method should only be directly invoked if you are absolutely sure the index is in bounds, to avoid a bounds check for a small boost of performance.

def unshift(value : T) : self #

Adds an item to the beginning of the deque.

    a = Deque{1, 2}
    a.unshift 0 # => Deque{0, 1, 2}