# The Sequence interface

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## Introduction

A Sequence describes the behaviour of values arranged in a single, linear dimension. Some languages refer to this as a "List". It’s similar to an array that uses incremental integer keys, with the exception of a few characteristics:

- Values will always be indexed as [0, 1, 2, …, size - 1].
- Only allowed to access values by index in the range [0, size - 1].

Use cases:

- Wherever you would use an array as a list (not concerned with keys).
- A more efficient alternative to SplDoublyLinkedList and SplFixedArray.

## Interface synopsis

Ds\Sequence implements Ds\Collection {
/* Methods */
abstract public allocate ( int `$capacity` ) : void
abstract public apply ( callable `$callback` ) : void
abstract public capacity ( void ) : int
abstract public contains ([ mixed `$...values` ] ) : bool
abstract public filter ([ callable `$callback` ] ) : Ds\Sequence
abstract public find ( mixed `$value` ) : mixed
abstract public first ( void ) : mixed
abstract public get ( int `$index` ) : mixed
abstract public insert ( int `$index` [, mixed `$...values` ] ) : void
abstract public join ([ string `$glue` ] ) : string
abstract public last ( void ) : mixed
abstract public map ( callable `$callback` ) : Ds\Sequence
abstract public merge ( mixed `$values` ) : Ds\Sequence
abstract public pop ( void ) : mixed
abstract public push ([ mixed `$...values` ] ) : void
abstract public reduce ( callable `$callback` [, mixed `$initial` ] ) : mixed
abstract public remove ( int `$index` ) : mixed
abstract public reverse ( void ) : void
abstract public reversed ( void ) : Ds\Sequence
abstract public rotate ( int `$rotations` ) : void
abstract public set ( int `$index` , mixed `$value` ) : void
abstract public shift ( void ) : mixed
abstract public slice ( int `$index` [, int `$length` ] ) : Ds\Sequence
abstract public sort ([ callable `$comparator` ] ) : void
abstract public sorted ([ callable `$comparator` ] ) : Ds\Sequence
abstract public sum ( void ) : number
abstract public unshift ([ mixed `$values` ] ) : void
}

## Table of Contents

- Ds\Sequence::allocate — Allocates enough memory for a required capacity
- Ds\Sequence::apply — Updates all values by applying a callback function to each value
- Ds\Sequence::capacity — Returns the current capacity
- Ds\Sequence::contains — Determines if the sequence contains given values
- Ds\Sequence::filter — Creates a new sequence using a callable to determine which values to include
- Ds\Sequence::find — Attempts to find a value's index
- Ds\Sequence::first — Returns the first value in the sequence
- Ds\Sequence::get — Returns the value at a given index
- Ds\Sequence::insert — Inserts values at a given index
- Ds\Sequence::join — Joins all values together as a string
- Ds\Sequence::last — Returns the last value
- Ds\Sequence::map — Returns the result of applying a callback to each value
- Ds\Sequence::merge — Returns the result of adding all given values to the sequence
- Ds\Sequence::pop — Removes and returns the last value
- Ds\Sequence::push — Adds values to the end of the sequence
- Ds\Sequence::reduce — Reduces the sequence to a single value using a callback function
- Ds\Sequence::remove — Removes and returns a value by index
- Ds\Sequence::reverse — Reverses the sequence in-place
- Ds\Sequence::reversed — Returns a reversed copy
- Ds\Sequence::rotate — Rotates the sequence by a given number of rotations
- Ds\Sequence::set — Updates a value at a given index
- Ds\Sequence::shift — Removes and returns the first value
- Ds\Sequence::slice — Returns a sub-sequence of a given range
- Ds\Sequence::sort — Sorts the sequence in-place
- Ds\Sequence::sorted — Returns a sorted copy
- Ds\Sequence::sum — Returns the sum of all values in the sequence
- Ds\Sequence::unshift — Adds values to the front of the sequence