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PHP 迭代器模式讲解和代码示例

迭代器是一种行为设计模式， 让你能在不暴露复杂数据结构内部细节的情况下遍历其中所有的元素。

在迭代器的帮助下， 客户端可以用一个迭代器接口以相似的方式遍历不同集合中的元素。

** 进一步了解迭代器模式 **

复杂度：******

流行度：******

使用示例： 该模式在 PHP 代码中很常见。 许多框架和程序库都会使用它来提供遍历其集合的标准方式。

PHP 拥有内置的迭代器接口， 可用于创建与其他 PHP 代码兼容的自定义迭代器。

识别方法： 迭代器可以通过导航方法 （例如 next和 previous等） 来轻松识别。 使用迭代器的客户端代码可能没有其所遍历的集合的直接访问权限。

概念示例真实世界示例

真实世界示例

由于 PHP 已有内置的迭代器接口并能方便地与 foreach 循环整合， 因此你很轻松就能为任何数据结构创建你自己的迭代器。

该迭代器模式示例可以轻松地访问 CSV 文件。

** index.php:  真实世界示例

<?php

namespace RefactoringGuru\Iterator\RealWorld;

/**
 * CSV File Iterator.
 *
 * @author Josh Lockhart
 */
class CsvIterator implements \Iterator
{
    const ROW_SIZE = 4096;

    /**
     * The pointer to the CSV file.
     *
     * @var resource
     */
    protected $filePointer = null;

    /**
     * The current element, which is returned on each iteration.
     *
     * @var array
     */
    protected $currentElement = null;

    /**
     * The row counter.
     *
     * @var int
     */
    protected $rowCounter = null;

    /**
     * The delimiter for the CSV file.
     *
     * @var string
     */
    protected $delimiter = null;

    /**
     * The constructor tries to open the CSV file. It throws an exception on
     * failure.
     *
     * @param string $file The CSV file.
     * @param string $delimiter The delimiter.
     *
     * @throws \Exception
     */
    public function __construct($file, $delimiter = ',')
    {
        try {
            $this->filePointer = fopen($file, 'rb');
            $this->delimiter = $delimiter;
        } catch (\Exception $e) {
            throw new \Exception('The file "' . $file . '" cannot be read.');
        }
    }

    /**
     * This method resets the file pointer.
     */
    public function rewind(): void
    {
        $this->rowCounter = 0;
        rewind($this->filePointer);
    }

    /**
     * This method returns the current CSV row as a 2-dimensional array.
     *
     * @return array The current CSV row as a 2-dimensional array.
     */
    public function current(): array
    {
        $this->currentElement = fgetcsv($this->filePointer, self::ROW_SIZE, $this->delimiter);
        $this->rowCounter++;

        return $this->currentElement;
    }

    /**
     * This method returns the current row number.
     *
     * @return int The current row number.
     */
    public function key(): int
    {
        return $this->rowCounter;
    }

    /**
     * This method checks if the end of file has been reached.
     *
     * @return bool Returns true on EOF reached, false otherwise.
     */
    public function next(): bool
    {
        if (is_resource($this->filePointer)) {
            return !feof($this->filePointer);
        }

        return false;
    }

    /**
     * This method checks if the next row is a valid row.
     *
     * @return bool If the next row is a valid row.
     */
    public function valid(): bool
    {
        if (!$this->next()) {
            if (is_resource($this->filePointer)) {
                fclose($this->filePointer);
            }

            return false;
        }

        return true;
    }
}

/**
 * The client code.
 */
$csv = new CsvIterator(__DIR__ . '/cats.csv');

foreach ($csv as $key => $row) {
    print_r($row);
}

** Output.txt:  执行结果

Array
(
    [0] => Name
    [1] => Age
    [2] => Owner
    [3] => Breed
    [4] => Image
    [5] => Color
    [6] => Texture
    [7] => Fur
    [8] => Size
)
Array
(
    [0] => Steve
    [1] => 3
    [2] => Alexander Shvets
    [3] => Bengal
    [4] => /cats/bengal.jpg
    [5] => Brown
    [6] => Stripes
    [7] => Short
    [8] => Medium
)
Array
(
    [0] => Siri
    [1] => 2
    [2] => Alexander Shvets
    [3] => Domestic short-haired
    [4] => /cats/domestic-sh.jpg
    [5] => Black
    [6] => Solid
    [7] => Medium
    [8] => Medium
)
Array
(
    [0] => Fluffy
    [1] => 5
    [2] => John Smith
    [3] => Maine Coon
    [4] => /cats/Maine-Coon.jpg
    [5] => Gray
    [6] => Stripes
    [7] => Long
    [8] => Large
)