PHP中的迭代器设计模式实例

迭代器设计模式被用来使一个对象可迭代，看起来像一个数组，而不暴露其内部细节。例如，一个复杂的数据结构被转化为一个可迭代的对象--如一个CSV文件。在下面的例子中，我们将模拟一个CSV文件的迭代，但以OOP方式进行。

类

线条

class Line
{
    private $id;
    private $name;
    private $surname;

    public function __construct(int $id, string $name, string $surname)
    {
        $this->id = $id;
        $this->name = $name;
        $this->surname = $surname;
    }

    public function getId(): int
    {
        return $this->id;
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function getSurname(): string
    {
        return $this->surname;
    }

    public function __toString(): string
    {
        return sprintf('%d, %s, %s', $this->id, $this->name, $this->surname);
    }
}

LineCollection

class LineCollection implements \Countable, \IteratorAggregate
{
    private $lines;

    public function getLines(): ?array
    {
        return $this->lines;
    }

    public function addLine(Line $line): self
    {
        $this->lines[] = $line;

        return $this;
    }

    public function removeLine(Line $line)
    {
        foreach ($this->lines as $key => $value) {
            if ($value === $line) {
                unset($this->lines[$key]);

                break;
            }
        }
    }

    public function count(): int
    {
        return count($this->lines);
    }

    public function getIterator(): LineIterator
    {
        return new LineIterator($this);
    }

    public function getReverseIterator(): LineIterator
    {
        return new LineIterator($this, true);
    }
}

线条迭代器

class LineIterator implements \Iterator
{
    private $lineCollection;
    private $position;
    private $reverse;

    public function __construct(LineCollection $lineCollection, bool $reverse = false)
    {
        $this->lineCollection = $lineCollection;
        $this->reverse = $reverse;
    }

    public function current(): ?Line
    {
        return $this->lineCollection->getLines()
            ? $this->lineCollection->getLines()[$this->position]
            : null;
    }

    public function next(): void
    {
        $this->position = $this->position + ($this->reverse ? -1 : 1);
    }

    public function key(): int
    {
        return is_null($this->position) ? 0 : $this->position;
    }

    public function valid(): bool
    {
        return $this->lineCollection->getLines() && isset($this->lineCollection->getLines()[$this->position]);
    }

    public function rewind(): void
    {
        $this->position = $this->reverse ? $this->lineCollection->count() - 1 : 0;
    }
}

用法

// Assume that this is a CSV file
$csvFile[0]['id'] = 1;
$csvFile[0]['name'] = 'John';
$csvFile[0]['surname'] = 'Travolta';
$csvFile[1]['id'] = 2;
$csvFile[1]['name'] = 'Robert';
$csvFile[1]['surname'] = 'De Niro';
//

// Populate collection
$lineCollection = new LineCollection();
foreach ($csvFile as $row) {
    $line = new Line($row['id'], $row['name'], $row['surname']);

    $lineCollection->addLine($line);
}
//

print_r($lineCollection);
echo PHP_EOL;

// Iterate in normal order
foreach ($lineCollection->getIterator() as $line) {
    echo $line->__toString().PHP_EOL;
}
//

echo PHP_EOL;

// Iterate in reverse order
foreach ($lineCollection->getReverseIterator() as $line) {
    echo $line->__toString().PHP_EOL;

    $lineCollection->removeLine($line); // Clear for demonstration purposes
}
//

echo PHP_EOL;
print_r($lineCollection);

结果

LineCollection Object
(
    [lines:LineCollection:private] => Array
        (
            [0] => Line Object
                (
                    [id:Line:private] => 1
                    [name:Line:private] => John
                    [surname:Line:private] => Travolta
                )

            [1] => Line Object
                (
                    [id:Line:private] => 2
                    [name:Line:private] => Robert
                    [surname:Line:private] => De Niro
                )
        )
)

1, John, Travolta
2, Robert, De Niro

2, Robert, De Niro
1, John, Travolta

LineCollection Object
(
    [lines:LineCollection:private] => Array
        (
        )
)