SeekableIterator インターフェイス

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

はじめに

Seekable イテレータです。

インターフェイス概要

interface SeekableIterator extends Iterator {

/* メソッド */

public function seek(int $offset): void

/* 継承したメソッド */

public function Iterator::current(): mixed

public function Iterator::key(): mixed

public function Iterator::next(): void

public function Iterator::rewind(): void

public function Iterator::valid(): bool

}

例

例1 基本的な使用法

この例では、SeekableIterator を作成して位置を移動し、無効な位置を扱います。

<?php
class MySeekableIterator implements SeekableIterator {

    private $position;

    private $array = array(
        "first element",
        "second element",
        "third element",
        "fourth element"
    );

    /* SeekableIterator インターフェイスで必要なメソッド群 */

    public function seek($position) {
      if (!isset($this->array[$position])) {
          throw new OutOfBoundsException("invalid seek position ($position)");
      }

      $this->position = $position;
    }

    /* Iterator インターフェイスで必要なメソッド群 */
    
    public function rewind() {
        $this->position = 0;
    }

    public function current() {
        return $this->array[$this->position];
    }

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

    public function next() {
        ++$this->position;
    }

    public function valid() {
        return isset($this->array[$this->position]);
    }
}

try {

    $it = new MySeekableIterator;
    echo $it->current(), "\n";
    
    $it->seek(2);
    echo $it->current(), "\n";
    
    $it->seek(1);
    echo $it->current(), "\n";
    
    $it->seek(10);
    
} catch (OutOfBoundsException $e) {
    echo $e->getMessage();
}
?>

上の例の出力は、たとえば以下のようになります。

first element
third element
second element
invalid seek position (10)

Best method:

<?php

if ($object instanceof SeekableIterator) {
  echo "\$object has method seek()";
}

?>

Please, make use of checking if a particular interface has been implemented to assure that the object you are dealing with definately has the methods you are about to use.

This also works as typehinting:

<?php

class foo {
  public function doSomeSeeking(SeekableIterator $seekMe) {
    $seekMe->seek(10); // will work, otherwise Typehint triggers complaints
  }
}

?>

down

info at ensostudio dot ru ¶

3 years ago

Note: $offset parameter of SeekableIterator::seek()  is position in list, not array key.
<?php
$iterator = new ArrayIterator([1 => "apple", 2 => "banana", 3 => "cherry"]);
echo $iterator->offsetGet(2); // banana
$iterator->seek(2);
echo $iterator->current(); // cherry
?>

down

-1

info at ensostudio dot ru ¶

5 years ago

Note: use array_key_exists instead isset!
<?php
public function seek($position)
{
    $position = (int) $position;
    if (! array_key_exists($position, array_values($this->array))) {
        throw new OutOfBoundsException('Invalid position to seek: ' . $position);
    }
    $this->position = $position;
}
?>

down

-2

Anonymous ¶

12 years ago

The code above is missing a closing parenthesis.

<?php
if (!isset($this->array[$position]) {
          throw new OutOfBoundsException("invalid seek position ($position)");
}
?>

should be

<?php
if (!isset($this->array[$position])) { // close here
          throw new OutOfBoundsException("invalid seek position ($position)");
}
?>

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SeekableIterator インターフェイス

はじめに

インターフェイス概要

例

目次

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User Contributed Notes 4 notes