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The CachingIterator class

(PHP 5, PHP 7)

Wstęp

This object supports cached iteration over another iterator.

Krótki opis klasy

CachingIterator extends IteratorIterator implements OuterIterator , ArrayAccess , Countable {

/* Stałe */

const integer CALL_TOSTRING = 1 ;

const integer CATCH_GET_CHILD = 16 ;

const integer TOSTRING_USE_KEY = 2 ;

const integer TOSTRING_USE_CURRENT = 4 ;

const integer TOSTRING_USE_INNER = 8 ;

const integer FULL_CACHE = 256 ;

/* Metody */

public __construct ( Iterator $iterator [, int $flags = self::CALL_TOSTRING ] )

public count ( void ) : int

public current ( void ) : mixed

public getCache ( void ) : array

public getFlags ( void ) : int

public getInnerIterator ( void ) : Iterator

public hasNext ( void ) : void

public key ( void ) : scalar

public next ( void ) : void

public offsetExists ( mixed $index ) : void

public offsetGet ( string $index ) : void

public offsetSet ( mixed $index , mixed $newval ) : void

public offsetUnset ( string $index ) : void

public rewind ( void ) : void

public setFlags ( int $flags ) : void

public __toString ( void ) : void

public valid ( void ) : void

}

Stałe predefiniowane

CachingIterator::CALL_TOSTRING: Convert every element to string.
CachingIterator::CATCH_GET_CHILD: Don't throw exception in accessing children.
CachingIterator::TOSTRING_USE_KEY: Use key for conversion to string.
CachingIterator::TOSTRING_USE_CURRENT: Use current for conversion to string.
CachingIterator::TOSTRING_USE_INNER: Use inner for conversion to string.
CachingIterator::FULL_CACHE: Cache all read data.

Spis treści

CachingIterator::__construct — Construct a new CachingIterator object for the iterator
CachingIterator::count — The number of elements in the iterator
CachingIterator::current — Return the current element
CachingIterator::getCache — Retrieve the contents of the cache
CachingIterator::getFlags — Get flags used
CachingIterator::getInnerIterator — Returns the inner iterator
CachingIterator::hasNext — Check whether the inner iterator has a valid next element
CachingIterator::key — Return the key for the current element
CachingIterator::next — Move the iterator forward
CachingIterator::offsetExists — The offsetExists purpose
CachingIterator::offsetGet — The offsetGet purpose
CachingIterator::offsetSet — The offsetSet purpose
CachingIterator::offsetUnset — The offsetUnset purpose
CachingIterator::rewind — Rewind the iterator
CachingIterator::setFlags — The setFlags purpose
CachingIterator::__toString — Return the string representation of the current element
CachingIterator::valid — Check whether the current element is valid

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User Contributed Notes 4 notes

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ahmad dot mayahi at gmail dot com ¶

7 years ago


<?php
//This snippet will print out all the cached elements (foreach) .

$cache  = new CachingIterator(new ArrayIterator(range(1,100)), CachingIterator::FULL_CACHE);

foreach ($cache as $c) {

}

print_r($cache->getCache());
?>

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ahmad dot mayahi at gmail dot com ¶

4 years ago


The only difference between CachingIterator and other Iterators such as ArrayIterator is the hasNext() method.

Since the data will be loaded into the memory, the CachingIterator is able to check whether the given iterator has a next element.

Let's demonstrate this by an example:

<?php
$iterator = new CachingIterator(new ArrayIterator(['C', 'C++', 'C#', 'PHP', 'Python', 'Go', 'Ruby']));

foreach ($iterator as $item) {
    if ($iterator->hasNext()) {
        echo $item.', ';
    } else {
        echo 'and '.$item;
    }
}

// C, C++, C#, PHP, Python, Go, and Ruby
?>

In this example I check whether the iterator has a next value, if so, I append a comma otherwise "and" will be appended to the last element.

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xedin dot unknown at gmail dot com ¶

3 years ago


Apparently, the `FULL_CACHE` flag automatically cancels the default flag `CALL_TOSTRING`. This is evident when one of the values cannot be converted to string: with the default `CALL_TOSTRING` flag, it would throw an error; without that flag, or with the `FULL_CACHE` flag, it does not.

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jerome at chaman dot ca ¶

4 years ago


"cached iteration over another iterator" means this iterator is always one step behind the inner iterator. In other words, the "first" iteration will yield null:

<?php

$cit = new CachingIterator( new ArrayIterator( [ 'a', 'b', 'c']  ) );

echo $cit->current() ); // null
echo $cit->getInnerIterator()->current() ); // "a"

while($cit->hasNext()){
    
    // we start with a "next" since the "first" item is null
     $cit->next();
     echo $cit->current(), '<br>';
   
}
?>

iterating this way gives us an access, ahead, to the future item (aka current item of the inner iterator)

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