在 PHP 中装饰迭代器 - 启用跳过

Question

我有一个 class，它基本上是 PHP 的 DirectoryIterator 的装饰器。每个文件的内容都由 class 处理，然后由 current() 方法 return 编辑。目前，当文件是点文件或无法处理文件时，我 return false 来自 current() 方法。但我宁愿跳过点和不可处理的文件，只处理 return 数据。

P.S。下面的代码是一个简化的例子。我不想在构造函数中预处理所有文件。

class Pages implements \Iterator
{
    public function __construct(string $path)
    {
        $this->di = new \DirectoryIterator($path);
    }

    public function rewind() {
        return $this->di->rewind();
    }

    public function current() {
        $file = $this->di->current();
        if($file->isDot()) {
            return false;
        }
        $content = file_get_contents($file->getPathName());
        if($content === 'Cannot be processed!') {
            return false;
        }
        return $content;
    }

    public function key() {
        return $this->di->key();
    }

    public function next() {
        return $this->di->next();
    }

    public function valid() {
        return $this->di->valid();
    }
}

Answer 1

我终于找到了这个解决方案，希望有人觉得它有用。可以将此模式应用于任何修饰的迭代器，有效地以类似于“过滤”迭代器的东西结束。

class FilteredIterator implements \Iterator
{
    protected $currentProcessed = null;
    protected $key = -1; // Keys are maintained by the decorating class

    public function __construct(Iterator $iterator)
    {
        $this->it = $iterator;
    }

    // Iterator interface START -->

    public function rewind() {
        $this->it->rewind();
        $this->forward();
    }

    public function current() {
        return $this->currentProcessed;
    }

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

    public function next() {
        $this->it->next();
        $this->forward();
    }

    public function valid() {
        return $this->it->valid();
    }

    // <-- Iterator interface END


    protected function forward() : void
    {
        if(!$this->it->valid()) {
            // Stop when iterator is done
            return;
        }
        // Pseudo code, insert expensive processing function here -->
        $content = $this->it->current();
        if($content === 5) {
        // <-- Pseudo code END
            // Skip 
            $this->next();
            return;
        }
        // Update position
        $this->key++;
        // Cache successfully processed step
        $this->currentProcessed = $content;

    }
}

$arrayObject = new ArrayObject([1,2,3,4,5,6]);

$filteredIterator = new FilteredIterator($arrayObject->getIterator());

foreach ($filteredIterator as $key => $value) {
    echo $key . ' -> ' . $value . "\n";
}

//0 -> 1
//1 -> 2
//2 -> 3
//3 -> 4
//4 -> 6

Answer 2

您可以通过扩展已经存在的摘要 PHP class FilterIterator :

来大大简化您自己的答案的代码

class DirectoryFilterIterator
  extends FilterIterator
{
  public function __construct(string $path) {
    parent::__construct(new DirectoryIterator($path));
  }

  public function accept() : bool {
    $current = parent::current();
    // let's not only ensure it's not a dot but that it's an actual readable file
    if(!$current->isFile() || !$current->isReadable()) {
      return false;
    }
    else {
      $contents = file_get_contents($current->getPathname());
      if($contents === 'Some value') {
        return false;
      }
    }
    
    return true;    
  }
}

foreach(new DirectoryFilterIterator('.') as $key => $value) {
  echo "$key -> $value\n";
}

如您所见，我不仅要确保该项目不是一个点，还要确保该项目是一个实际可读的文件，因为我认为这更符合您的意图。

PS：由于您的初衷是创建一个 decorator/wrapper，因此您当然可以更改 DirectoryFilterIterator 的构造函数以接受 DirectoryIterator：

public function __construct(DirectoryIterator $it) {
  parent::__construct($it);
}

...然后将实例化更改为：

foreach(new DirectoryFilterIterator(new DirectoryIterator('.')) as $key => $value) {
  echo "$key -> $value\n";
}

在 PHP 中装饰迭代器 - 启用跳过

Decorate an Iterator in PHP - enable skipping

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