(PHP 5 >= 5.1.0, PHP 7, PHP 8)
The Seekable iterator.
Example #1 Basic usage
This example demonstrates creating a custom SeekableIterator, seeking to a position and handling an invalid position.
<?php
class MySeekableIterator implements SeekableIterator {
private $position;
private $array = array(
"first element",
"second element",
"third element",
"fourth element"
);
/* Method required for SeekableIterator interface */
public function seek($position) {
if (!isset($this->array[$position])) {
throw new OutOfBoundsException("invalid seek position ($position)");
}
$this->position = $position;
}
/* Methods required for Iterator interface */
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 $e->getMessage();
}
?>
以上例程的输出类似于：
first element third element second element invalid seek position (10)
Note: use array_key_exists instead isset!
<?php
public function seek($position)
{
$position = (int) $position;
if (! array_key_exists($position, array_values($this->array))) {
throw new OutOfBoundsException('Invalid position to seek: ' . $position);
}
$this->position = $position;
}
?>
The code above is missing a closing parenthesis.
<?php
if (!isset($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 ($position)");
}
?>
Best method:
<?php
if ($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
}
}
?>
The reflection approach:
<?php
$reflection = new ReflectionClass('MySeekableIterator');
if($reflection->hasMethod('seek'))
echo "This class has method seek().";
?>
Better method:
<?php
$class = 'SeekableIterator';
$findingMethod = 'seek'; // have to be lower chars
$methods = get_class_methods($class);
foreach( $methods as $pVal )
if ( $findingMethod == strtolower($pVal) ) {
echo 'This class has method seek().';
break;
}
}
?>
Best method: http://php.net/manual/en/function.method-exists.php