<?php

/**
 * This file is part of the ramsey/collection library
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 *
 * @copyright Copyright (c) Ben Ramsey <ben@benramsey.com>
 * @license http://opensource.org/licenses/MIT MIT
 */

declare(strict_types=1);

namespace Ramsey\Collection;

use Ramsey\Collection\Exception\NoSuchElementException;
use RuntimeException;

/**
 * A queue is a collection in which the entities in the collection are kept in
 * order.
 *
 * The principal operations on the queue are the addition of entities to the end
 * (tail), also known as *enqueue*, and removal of entities from the front
 * (head), also known as *dequeue*. This makes the queue a first-in-first-out
 * (FIFO) data structure.
 *
 * Besides basic array operations, queues provide additional insertion,
 * extraction, and inspection operations. Each of these methods exists in two
 * forms: one throws an exception if the operation fails, the other returns a
 * special value (either `null` or `false`, depending on the operation). The
 * latter form of the insert operation is designed specifically for use with
 * capacity-restricted `QueueInterface` implementations; in most
 * implementations, insert operations cannot fail.
 *
 * <table>
 * <caption>Summary of QueueInterface methods</caption>
 * <thead>
 * <tr>
 * <td></td>
 * <td><em>Throws exception</em></td>
 * <td><em>Returns special value</em></td>
 * </tr>
 * </thead>
 * <tbody>
 * <tr>
 * <th>Insert</th>
 * <td><code>add()</code></td>
 * <td><code>offer()</code></td>
 * </tr>
 * <tr>
 * <th>Remove</th>
 * <td><code>remove()</code></td>
 * <td><code>poll()</code></td>
 * </tr>
 * <tr>
 * <th>Examine</th>
 * <td><code>element()</code></td>
 * <td><code>peek()</code></td>
 * </tr>
 * </tbody>
 * </table>
 *
 * Queues typically, but do not necessarily, order elements in a FIFO
 * (first-in-first-out) manner. Among the exceptions are priority queues, which
 * order elements according to a supplied comparator, or the elements' natural
 * ordering, and LIFO queues (or stacks) which order the elements LIFO
 * (last-in-first-out). Whatever the ordering used, the head of the queue is
 * that element which would be removed by a call to remove() or poll(). In a
 * FIFO queue, all new elements are inserted at the tail of the queue. Other
 * kinds of queues may use different placement rules. Every `QueueInterface`
 * implementation must specify its ordering properties.
 *
 * The `offer()` method inserts an element if possible, otherwise returning
 * `false`. This differs from the `add()` method, which can fail to add an
 * element only by throwing an unchecked exception. The `offer()` method is
 * designed for use when failure is a normal, rather than exceptional
 * occurrence, for example, in fixed-capacity (or "bounded") queues.
 *
 * The `remove()` and `poll()` methods remove and return the head of the queue.
 * Exactly which element is removed from the queue is a function of the queue's
 * ordering policy, which differs from implementation to implementation. The
 * `remove()` and `poll()` methods differ only in their behavior when the queue
 * is empty: the `remove()` method throws an exception, while the `poll()`
 * method returns `null`.
 *
 * The `element()` and `peek()` methods return, but do not remove, the head of
 * the queue.
 *
 * `QueueInterface` implementations generally do not allow insertion of `null`
 * elements, although some implementations do not prohibit insertion of `null`.
 * Even in the implementations that permit it, `null` should not be inserted
 * into a queue, as `null` is also used as a special return value by the
 * `poll()` method to indicate that the queue contains no elements.
 *
 * @template T
 * @extends ArrayInterface<T>
 */
interface QueueInterface extends ArrayInterface
{
    /**
     * Ensures that this queue contains the specified element (optional
     * operation).
     *
     * Returns `true` if this queue changed as a result of the call. (Returns
     * `false` if this queue does not permit duplicates and already contains the
     * specified element.)
     *
     * Queues that support this operation may place limitations on what elements
     * may be added to this queue. In particular, some queues will refuse to add
     * `null` elements, and others will impose restrictions on the type of
     * elements that may be added. Queue classes should clearly specify in their
     * documentation any restrictions on what elements may be added.
     *
     * If a queue refuses to add a particular element for any reason other than
     * that it already contains the element, it must throw an exception (rather
     * than returning `false`). This preserves the invariant that a queue always
     * contains the specified element after this call returns.
     *
     * @see self::offer()
     *
     * @param T $element The element to add to this queue.
     *
     * @return bool `true` if this queue changed as a result of the call.
     *
     * @throws RuntimeException if a queue refuses to add a particular element
     *     for any reason other than that it already contains the element.
     *     Implementations should use a more-specific exception that extends
     *     `\RuntimeException`.
     */
    public function add(mixed $element): bool;

    /**
     * Retrieves, but does not remove, the head of this queue.
     *
     * This method differs from `peek()` only in that it throws an exception if
     * this queue is empty.
     *
     * @see self::peek()
     *
     * @return T the head of this queue.
     *
     * @throws NoSuchElementException if this queue is empty.
     */
    public function element(): mixed;

    /**
     * Inserts the specified element into this queue if it is possible to do so
     * immediately without violating capacity restrictions.
     *
     * When using a capacity-restricted queue, this method is generally
     * preferable to `add()`, which can fail to insert an element only by
     * throwing an exception.
     *
     * @see self::add()
     *
     * @param T $element The element to add to this queue.
     *
     * @return bool `true` if the element was added to this queue, else `false`.
     */
    public function offer(mixed $element): bool;

    /**
     * Retrieves, but does not remove, the head of this queue, or returns `null`
     * if this queue is empty.
     *
     * @see self::element()
     *
     * @return T | null the head of this queue, or `null` if this queue is empty.
     */
    public function peek(): mixed;

    /**
     * Retrieves and removes the head of this queue, or returns `null`
     * if this queue is empty.
     *
     * @see self::remove()
     *
     * @return T | null the head of this queue, or `null` if this queue is empty.
     */
    public function poll(): mixed;

    /**
     * Retrieves and removes the head of this queue.
     *
     * This method differs from `poll()` only in that it throws an exception if
     * this queue is empty.
     *
     * @see self::poll()
     *
     * @return T the head of this queue.
     *
     * @throws NoSuchElementException if this queue is empty.
     */
    public function remove(): mixed;

    /**
     * Returns the type associated with this queue.
     */
    public function getType(): string;
}

.NET Framework

Project Request

ProjectC

Vehicle Maintenance

Movie Navigator

Customers Exchange

ATM

.NET Core

Mail Daemon

Custom

Buns of code

PHP

Mediabox

Loan Castle

Content Management

Laravel

Phone Check

Frontend

Forex Wall

Business projects

Certification Center

Amerikas Auto

Pet projects

Geolocation Assistant

Web Dynamics

Blackball

Good old times

DOS Clock

BrainOut

Airport Administrator

Atomizer

Mediabox