The Deque class

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Introduction

A Deque (pronounced “deck”) is a sequence of values in a contiguous buffer that grows and shrinks automatically. The name is a common abbreviation of “double-ended queue” and is used internally by Ds\Queue.

Two pointers are used to keep track of a head and a tail. The pointers can “wrap around” the end of the buffer, which avoids the need to move other values around to make room. This makes shift and unshift very fast — something a Ds\Vector can’t compete with.

Accessing a value by index requires a translation between the index and its corresponding position in the buffer: ((head + position) % capacity).

Strengths

Supports array syntax (square brackets).
Uses less overall memory than an array for the same number of values.
Automatically frees allocated memory when its size drops low enough.
get(), set(), push(), pop(), shift(), and unshift() are all O(1).

Weaknesses

Capacity must be a power of 2.
insert() and remove() are O(n).

Class synopsis

class Ds\Deque implements Ds\Sequence, ArrayAccess {

/* Constants */

const int MIN_CAPACITY = 8;

/* Methods */

public allocate(int $capacity): void

public apply(callable $callback): void

public capacity(): int

public clear(): void

public contains(mixed ...$values): bool

public copy(): Ds\Deque

public filter(callable $callback = ?): Ds\Deque

public find(mixed $value): mixed

public first(): mixed

public get(int $index): mixed

public insert(int $index, mixed ...$values): void

public isEmpty(): bool

public join(string $glue = ?): string

public last(): mixed

public map(callable $callback): Ds\Deque

public merge(mixed $values): Ds\Deque

public pop(): mixed

public push(mixed ...$values): void

public reduce(callable $callback, mixed $initial = ?): mixed

public remove(int $index): mixed

public reverse(): void

public reversed(): Ds\Deque

public rotate(int $rotations): void

public set(int $index, mixed $value): void

public shift(): mixed

public slice(int $index, int $length = ?): Ds\Deque

public sort(callable $comparator = ?): void

public sorted(callable $comparator = ?): Ds\Deque

public sum(): int|float

public toArray(): array

public unshift(mixed $values = ?): void

}

Predefined Constants

Ds\Deque::MIN_CAPACITY

Changelog

Version	Description
PECL ds 1.3.0	The class now implements ArrayAccess.

Ds\Deque::allocate — Allocates enough memory for a required capacity
Ds\Deque::apply — Updates all values by applying a callback function to each value
Ds\Deque::capacity — Returns the current capacity
Ds\Deque::clear — Removes all values from the deque
Ds\Deque::__construct — Creates a new instance
Ds\Deque::contains — Determines if the deque contains given values
Ds\Deque::copy — Returns a shallow copy of the deque
Ds\Deque::count — Returns the number of values in the collection
Ds\Deque::filter — Creates a new deque using a callable to determine which values to include
Ds\Deque::find — Attempts to find a value's index
Ds\Deque::first — Returns the first value in the deque
Ds\Deque::get — Returns the value at a given index
Ds\Deque::insert — Inserts values at a given index
Ds\Deque::isEmpty — Returns whether the deque is empty
Ds\Deque::join — Joins all values together as a string
Ds\Deque::jsonSerialize — Returns a representation that can be converted to JSON
Ds\Deque::last — Returns the last value
Ds\Deque::map — Returns the result of applying a callback to each value
Ds\Deque::merge — Returns the result of adding all given values to the deque
Ds\Deque::pop — Removes and returns the last value
Ds\Deque::push — Adds values to the end of the deque
Ds\Deque::reduce — Reduces the deque to a single value using a callback function
Ds\Deque::remove — Removes and returns a value by index
Ds\Deque::reverse — Reverses the deque in-place
Ds\Deque::reversed — Returns a reversed copy
Ds\Deque::rotate — Rotates the deque by a given number of rotations
Ds\Deque::set — Updates a value at a given index
Ds\Deque::shift — Removes and returns the first value
Ds\Deque::slice — Returns a sub-deque of a given range
Ds\Deque::sort — Sorts the deque in-place
Ds\Deque::sorted — Returns a sorted copy
Ds\Deque::sum — Returns the sum of all values in the deque
Ds\Deque::toArray — Converts the deque to an array
Ds\Deque::unshift — Adds values to the front of the deque