PHP设计模式组合与迭代器

PHP设计模式组合与迭代器

组合模式和迭代器模式都是结构型设计模式。组合模式让客户端统一处理单个对象和组合对象，迭代器提供遍历集合的标准方式。今天说说这两种模式。

组合模式在树形结构中很有用。

```php
abstract class FileSystemComponent
{
protected string $name;
public function __construct(string $name) { $this->name = $name; }
abstract public function getSize(): int;
abstract public function display(int $depth = 0): void;
}

class File extends FileSystemComponent
{
private int $size;

public function __construct(string $name, int $size)
{
parent::__construct($name);
$this->size = $size;
}

public function getSize(): int { return $this->size; }

public function display(int $depth = 0): void
{
echo str_repeat(" ", $depth) . "📄 {$this->name} ({$this->size}KB)\n";
}
}

class Directory extends FileSystemComponent
{
private array $children = [];

public function add(FileSystemComponent $component): void
{
$this->children[] = $component;
}

public function getSize(): int
{
$total = 0;
foreach ($this->children as $child) $total += $child->getSize();
return $total;
}

public function display(int $depth = 0): void
{
echo str_repeat(" ", $depth) . "📁 {$this->name}/\n";
foreach ($this->children as $child) $child->display($depth + 1);
}
}

$root = new Directory("root");
$home = new Directory("home");
$home->add(new File("readme.txt", 10));
$home->add(new File("photo.jpg", 500));
$root->add($home);
$root->add(new File("config.php", 50));

$root->display();
echo "总大小: {$root->getSize()}KB\n";
?>

迭代器提供统一的遍历方式。

```php
class RangeIterator implements Iterator
{
private int $current;
private int $end;
private int $step;

public function __construct(int $start, int $end, int $step = 1)
{
$this->current = $start;
$this->end = $end;
$this->step = $step;
}

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

public function next(): void
{
$this->current += $this->step;
}

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

public function valid(): bool
{
return $this->current <= $this->end;
}
}

foreach (new RangeIterator(1, 5) as $num) {
echo "$num ";
}
echo "\n";
?>

组合模式让叶子节点和容器节点有统一的接口。迭代器让集合的遍历方式统一。两种模式在框架和库中广泛应用，PHP的SPL提供了多种迭代器实现。