The CachingIterator class

(PHP 5, PHP 7, PHP 8)

简介

This object supports cached iteration over another iterator.

类摘要

CachingIterator extends IteratorIterator implements OuterIterator , ArrayAccess , Countable {

/* 常量 */

const int CALL_TOSTRING = 1 ;

const int CATCH_GET_CHILD = 16 ;

const int TOSTRING_USE_KEY = 2 ;

const int TOSTRING_USE_CURRENT = 4 ;

const int TOSTRING_USE_INNER = 8 ;

const int FULL_CACHE = 256 ;

/* 方法 */

public __construct ( Iterator $iterator , int $flags = CachingIterator::CALL_TOSTRING )

public count ( ) : int

public current ( ) : mixed

public getCache ( ) : array

public getFlags ( ) : int

public getInnerIterator ( ) : Iterator

public hasNext ( ) : bool

public key ( ) : scalar

public next ( ) : void

public offsetExists ( string $key ) : bool

public offsetGet ( string $key ) : mixed

public offsetSet ( string $key , mixed $value ) : void

public offsetUnset ( string $key ) : void

public rewind ( ) : void

public setFlags ( int $flags ) : void

public __toString ( ) : string

public valid ( ) : bool

}

预定义常量

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.

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

User Contributed Notes

xedin dot unknown at gmail dot com 07-May-2020 05:19


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.

ahmad dot mayahi at gmail dot com 25-Apr-2020 09:53


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.

jerome at chaman dot ca 15-Dec-2019 12:37


"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)

ahmad dot mayahi at gmail dot com 24-Oct-2016 07:54


<?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());

?>

The CachingIterator class

简介

类摘要

预定义常量

Table of Contents

User Contributed Notes