317 lines
10 KiB
PHP
317 lines
10 KiB
PHP
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<?php
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/**
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* This file is part of the ramsey/collection library
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*
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* @copyright Copyright (c) Ben Ramsey <ben@benramsey.com>
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* @license http://opensource.org/licenses/MIT MIT
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*/
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declare(strict_types=1);
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namespace Ramsey\Collection;
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use Ramsey\Collection\Exception\NoSuchElementException;
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/**
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* A linear collection that supports element insertion and removal at both ends.
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*
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* Most `DoubleEndedQueueInterface` implementations place no fixed limits on the
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* number of elements they may contain, but this interface supports
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* capacity-restricted double-ended queues as well as those with no fixed size
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* limit.
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*
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* This interface defines methods to access the elements at both ends of the
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* double-ended queue. Methods are provided to insert, remove, and examine the
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* element. Each of these methods exists in two forms: one throws an exception
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* if the operation fails, the other returns a special value (either `null` or
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* `false`, depending on the operation). The latter form of the insert operation
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* is designed specifically for use with capacity-restricted implementations; in
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* most implementations, insert operations cannot fail.
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*
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* The twelve methods described above are summarized in the following table:
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*
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* <table>
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* <caption>Summary of DoubleEndedQueueInterface methods</caption>
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* <thead>
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* <tr>
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* <th></th>
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* <th colspan=2>First Element (Head)</th>
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* <th colspan=2>Last Element (Tail)</th>
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* </tr>
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* <tr>
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* <td></td>
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* <td><em>Throws exception</em></td>
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* <td><em>Special value</em></td>
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* <td><em>Throws exception</em></td>
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* <td><em>Special value</em></td>
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* </tr>
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* </thead>
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* <tbody>
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* <tr>
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* <th>Insert</th>
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* <td><code>addFirst()</code></td>
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* <td><code>offerFirst()</code></td>
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* <td><code>addLast()</code></td>
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* <td><code>offerLast()</code></td>
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* </tr>
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* <tr>
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* <th>Remove</th>
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* <td><code>removeFirst()</code></td>
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* <td><code>pollFirst()</code></td>
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* <td><code>removeLast()</code></td>
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* <td><code>pollLast()</code></td>
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* </tr>
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* <tr>
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* <th>Examine</th>
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* <td><code>firstElement()</code></td>
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* <td><code>peekFirst()</code></td>
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* <td><code>lastElement()</code></td>
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* <td><code>peekLast()</code></td>
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* </tr>
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* </tbody>
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* </table>
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*
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* This interface extends the `QueueInterface`. When a double-ended queue is
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* used as a queue, FIFO (first-in-first-out) behavior results. Elements are
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* added at the end of the double-ended queue and removed from the beginning.
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* The methods inherited from the `QueueInterface` are precisely equivalent to
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* `DoubleEndedQueueInterface` methods as indicated in the following table:
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*
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* <table>
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* <caption>Comparison of QueueInterface and DoubleEndedQueueInterface methods</caption>
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* <thead>
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* <tr>
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* <th>QueueInterface Method</th>
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* <th>DoubleEndedQueueInterface Method</th>
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* </tr>
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* </thead>
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* <tbody>
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* <tr>
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* <td><code>add()</code></td>
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* <td><code>addLast()</code></td>
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* </tr>
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* <tr>
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* <td><code>offer()</code></td>
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* <td><code>offerLast()</code></td>
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* </tr>
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* <tr>
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* <td><code>remove()</code></td>
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* <td><code>removeFirst()</code></td>
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* </tr>
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* <tr>
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* <td><code>poll()</code></td>
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* <td><code>pollFirst()</code></td>
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* </tr>
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* <tr>
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* <td><code>element()</code></td>
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* <td><code>firstElement()</code></td>
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* </tr>
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* <tr>
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* <td><code>peek()</code></td>
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* <td><code>peekFirst()</code></td>
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* </tr>
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* </tbody>
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* </table>
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*
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* Double-ended queues can also be used as LIFO (last-in-first-out) stacks. When
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* a double-ended queue is used as a stack, elements are pushed and popped from
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* the beginning of the double-ended queue. Stack concepts are precisely
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* equivalent to `DoubleEndedQueueInterface` methods as indicated in the table
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* below:
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*
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* <table>
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* <caption>Comparison of stack concepts and DoubleEndedQueueInterface methods</caption>
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* <thead>
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* <tr>
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* <th>Stack concept</th>
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* <th>DoubleEndedQueueInterface Method</th>
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* </tr>
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* </thead>
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* <tbody>
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* <tr>
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* <td><em>push</em></td>
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* <td><code>addFirst()</code></td>
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* </tr>
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* <tr>
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* <td><em>pop</em></td>
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* <td><code>removeFirst()</code></td>
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* </tr>
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* <tr>
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* <td><em>peek</em></td>
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* <td><code>peekFirst()</code></td>
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* </tr>
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* </tbody>
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* </table>
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*
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* Note that the `peek()` method works equally well when a double-ended queue is
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* used as a queue or a stack; in either case, elements are drawn from the
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* beginning of the double-ended queue.
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*
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* While `DoubleEndedQueueInterface` implementations are not strictly required
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* to prohibit the insertion of `null` elements, they are strongly encouraged to
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* do so. Users of any `DoubleEndedQueueInterface` implementations that do allow
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* `null` elements are strongly encouraged *not* to take advantage of the
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* ability to insert nulls. This is so because `null` is used as a special
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* return value by various methods to indicated that the double-ended queue is
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* empty.
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*
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* @template T
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* @template-extends QueueInterface<T>
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*/
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interface DoubleEndedQueueInterface extends QueueInterface
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{
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/**
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* Inserts the specified element at the front of this queue if it is
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* possible to do so immediately without violating capacity restrictions.
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*
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* When using a capacity-restricted double-ended queue, it is generally
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* preferable to use the `offerFirst()` method.
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*
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* @param T $element The element to add to the front of this queue.
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*
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* @return bool `true` if this queue changed as a result of the call.
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*
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* @throws \RuntimeException if a queue refuses to add a particular element
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* for any reason other than that it already contains the element.
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* Implementations should use a more-specific exception that extends
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* `\RuntimeException`.
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*/
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// phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
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public function addFirst($element): bool;
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/**
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* Inserts the specified element at the end of this queue if it is possible
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* to do so immediately without violating capacity restrictions.
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*
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* When using a capacity-restricted double-ended queue, it is generally
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* preferable to use the `offerLast()` method.
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*
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* This method is equivalent to `add()`.
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*
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* @param T $element The element to add to the end of this queue.
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*
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* @return bool `true` if this queue changed as a result of the call.
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*
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* @throws \RuntimeException if a queue refuses to add a particular element
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* for any reason other than that it already contains the element.
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* Implementations should use a more-specific exception that extends
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* `\RuntimeException`.
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*/
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// phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
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public function addLast($element): bool;
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/**
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* Inserts the specified element at the front of this queue if it is
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* possible to do so immediately without violating capacity restrictions.
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*
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* When using a capacity-restricted queue, this method is generally
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* preferable to `addFirst()`, which can fail to insert an element only by
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* throwing an exception.
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*
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* @param T $element The element to add to the front of this queue.
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*
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* @return bool `true` if the element was added to this queue, else `false`.
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*/
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// phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
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public function offerFirst($element): bool;
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/**
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* Inserts the specified element at the end of this queue if it is possible
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* to do so immediately without violating capacity restrictions.
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*
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* When using a capacity-restricted queue, this method is generally
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* preferable to `addLast()` which can fail to insert an element only by
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* throwing an exception.
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*
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* @param T $element The element to add to the end of this queue.
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*
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* @return bool `true` if the element was added to this queue, else `false`.
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*/
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// phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
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public function offerLast($element): bool;
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/**
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* Retrieves and removes the head of this queue.
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*
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* This method differs from `pollFirst()` only in that it throws an
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* exception if this queue is empty.
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*
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* @return T the first element in this queue.
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*
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* @throws NoSuchElementException if this queue is empty.
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*/
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public function removeFirst();
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/**
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* Retrieves and removes the tail of this queue.
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*
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* This method differs from `pollLast()` only in that it throws an exception
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* if this queue is empty.
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*
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* @return T the last element in this queue.
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*
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* @throws NoSuchElementException if this queue is empty.
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*/
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public function removeLast();
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/**
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* Retrieves and removes the head of this queue, or returns `null` if this
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* queue is empty.
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*
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* @return T|null the head of this queue, or `null` if this queue is empty.
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*/
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public function pollFirst();
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/**
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* Retrieves and removes the tail of this queue, or returns `null` if this
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* queue is empty.
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*
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* @return T|null the tail of this queue, or `null` if this queue is empty.
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*/
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public function pollLast();
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/**
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* Retrieves, but does not remove, the head of this queue.
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*
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* This method differs from `peekFirst()` only in that it throws an
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* exception if this queue is empty.
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*
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* @return T the head of this queue.
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*
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* @throws NoSuchElementException if this queue is empty.
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*/
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public function firstElement();
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/**
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* Retrieves, but does not remove, the tail of this queue.
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*
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* This method differs from `peekLast()` only in that it throws an exception
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* if this queue is empty.
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*
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* @return T the tail of this queue.
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*
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* @throws NoSuchElementException if this queue is empty.
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*/
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public function lastElement();
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/**
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* Retrieves, but does not remove, the head of this queue, or returns `null`
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* if this queue is empty.
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*
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* @return T|null the head of this queue, or `null` if this queue is empty.
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*/
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public function peekFirst();
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/**
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* Retrieves, but does not remove, the tail of this queue, or returns `null`
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* if this queue is empty.
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*
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* @return T|null the tail of this queue, or `null` if this queue is empty.
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*/
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public function peekLast();
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}
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