PHP数据集合与迭代器模式

PHP数据集合与迭代器模式

集合和迭代器用于统一处理数据集合。PHP的SPL提供了多种迭代器实现。今天说说PHP中集合和迭代器的用法。

PHP的Iterator接口提供了遍历集合的标准方式。

```php
class FileLineIterator implements Iterator
{
private $handle;
private int $key = 0;
private ?string $current = null;

public function __construct(private string $path)
{
$this->handle = fopen($path, 'r');
if ($this->handle === false) throw new RuntimeException("无法打开文件: $path");
$this->next();
}

public function current(): mixed { return $this->current; }
public function key(): mixed { return $this->key; }

public function next(): void
{
if (!feof($this->handle)) {
$this->current = fgets($this->handle);
$this->key++;
} else {
$this->current = null;
}
}

public function rewind(): void
{
rewind($this->handle);
$this->key = 0;
$this->next();
}

public function valid(): bool
{
return $this->current !== false && $this->current !== null;
}

public function __destruct()
{
if ($this->handle) fclose($this->handle);
}
}

file_put_contents('/tmp/data.txt', "行1\n行2\n行3\n");
foreach (new FileLineIterator('/tmp/data.txt') as $lineNum => $line) {
echo "{$lineNum}: " . trim($line) . "\n";
}
?>
>

PHP的集合类封装了数组操作。

```php
class Collection
{
private array $items = [];

public function __construct(array $items = [])
{
$this->items = $items;
}

public function add(mixed $item): void
{
$this->items[] = $item;
}

public function map(callable $callback): self
{
return new self(array_map($callback, $this->items));
}

public function filter(callable $callback): self
{
return new self(array_values(array_filter($this->items, $callback)));
}

public function reduce(callable $callback, mixed $initial = null): mixed
{
return array_reduce($this->items, $callback, $initial);
}

public function first(): mixed
{
return !empty($this->items) ? $this->items[0] : null;
}

public function last(): mixed
{
return !empty($this->items) ? $this->items[count($this->items) - 1] : null;
}

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

public function toArray(): array
{
return $this->items;
}

public function isEmpty(): bool
{
return empty($this->items);
}

public function chunk(int $size): array
{
$chunks = [];
foreach (array_chunk($this->items, $size) as $chunk) {
$chunks[] = new self($chunk);
}
return $chunks;
}
}

$collection = new Collection([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

$result = $collection
->filter(fn($v) => $v % 2 === 0)
->map(fn($v) => $v * $v);

print_r($result->toArray());
echo "总数: " . $result->count() . "\n";
?>

SPL提供的迭代器类。

```php
// 递归目录迭代器
$files = new RecursiveIteratorIterator(
new RecursiveDirectoryIterator('/tmp')
);

foreach ($files as $file) {
if ($file->isFile()) {
echo $file->getPathname() . " (" . $file->getSize() . "字节)\n";
}
}

// 数组迭代器
$iterator = new ArrayIterator(['a' => 1, 'b' => 2, 'c' => 3]);
foreach ($iterator as $key => $value) {
echo "$key => $value\n";
}

// 过滤迭代器
$filtered = new CallbackFilterIterator(
new ArrayIterator([1, 2, 3, 4, 5]),
fn($v) => $v % 2 === 0
);
foreach ($filtered as $v) echo "$v ";
echo "\n";
?>

Iterator和Collection模式让数据集合的处理更加统一。无论是数组、文件还是数据库结果集，都可以用统一的接口遍历。SPL提供了丰富的迭代器类，可以处理各种数据结构。