The document provides an introduction to the Standard PHP Library (SPL), detailing its purpose, which includes offering reusable components and helpful data structures for common programming problems. It discusses various features such as iterators, data structures introduced in PHP 5.2 and 5.3, and exceptions, emphasizing their utility and implementation in PHP. Additionally, it covers the benefits of using iterators and SPL's extensions while promoting community engagement through events like testfests.

1.
An Introduction to SPL ,
the S tandard P HP L ibrary
Robin Fernandes ( [email_address] / @rewbs )

2.
What is SPL?
A collection of classes and interfaces for solving common programming problems .
Useful data structures
Loads of iterators
General-purpose exception hierarchy
& more...

3.
Why use SPL?
Helps you write less code
Provides reusable components
Provides recognisable behaviour
It's relatively fast
It's well tested (soon to be extremely well tested)
Zend
Framework
Agavi

4.
SPL Documentation
Some info here:
http://php.net/spl
More info here:
http://php.net/~helly
Also see PHP code in cvs:
ext/spl/examples/*.php, *.inc
ext/spl/internal/*.php, *.inc

5.
SPL Data Structures
In PHP 5.2 :
ArrayObject -> OO array wrapper – extend it!
SplObjectStorage -> Dictionary with objects as keys
SplFileObject -> OO stream wrapper
New in PHP 5.3 :
SplDoublyLinkedList
SplStack -> Last In First Out
SplHeap -> Binary heap
SplMaxHeap, SplMinHeap
SplQueue -> First In First Out
SplPriorityQueue
SplFixedArray -> aka SplFastArray: C array of zval

6.
Iterators
What's an Iterator?
An iterator implements a consistent interface for traversing a collection .
Why Use Iterators?
Iterators decouple collections from algorithms by encapsulating traversal logic.

7.
Without Iterators
...
...
Algorithms:
...
...
...
...
...
...
Sum:
Average:
Display:
Collections:
1
2
3
4
1
4
5
3
2

8.
With Iterators
...
Collections:
Algorithms:
...
Iterators:
Algorithms are
decoupled
from collections!
1
2
3
4
1
4
5
3
2

9.
Iterators in PHP
To create your own iterator class, implement Iterator :
To make a collection class iterable using a distinct iterator, implement IteratorAggregate :
interface Iterator extends Traversable {
function rewind();
function valid();
function current();
function key();
function next();
}
interface IteratorAggregate extends Traversable {
function getIterator();
}

10.
Iterators in PHP
class MyList
implements IteratorAggregate {
private $nodes = ...;
function getIterator() {
return new MyListIterator( $this );
}
}
class MyGraph
implements IteratorAggregate {
private $nodes = ...;
private $edges = ...;
function getIterator() {
return new MyGraphIterator( $this );
}
}
function show( $collection ) {
foreach ( $collection as $node ) {
echo &quot; $node <br/>&quot; ;
}
}
echo show( new MyList);
echo show( new MyGraph);

11.
Iterators in PHP
Traversable objects get special foreach treatment :
foreach ( $traversableObj as $key => $value ) {
// Loop body
}
// 1. Get the Iterator instance from $traversableObj:
if ( $traversableObj instanceof Iterator) {
$iterator = $traversableObj ;
} else if ( $traversableObj instanceof IteratorAggregate){
$iterator = $traversableObj ->getIterator();
}
// 2. Loop using the methods provided by Iterator:
$iterator ->rewind();
while ( $iterator ->valid()) {
$value = $iterator ->current();
$key = $iterator ->key();
// Loop body
$iterator ->next();
}
<=>
… is equivalent to ...
Note:
- User-space classes can't implement Traversable directly.
- No class can implement both Iterator and IteratorAggregate.

12.
SPL Iterators
Iterator decorators:
AppendIterator
CachingIterator
FilterIterator
InfiniteIterator
IteratorIterator
LimitIterator
MultipleIterator (5.3)
NoRewindIterator
ParentIterator
RegexIterator
RecursiveIteratorIterator
RecursiveCachingIterator
RecursiveFilterIterator
RecursiveRegexIterator
RecursiveTreeIterator (5.3)
Concrete iterators:
ArrayIterator
RecursiveArrayIterator
DirectoryIterator
RecursiveDirectoryIterator
EmptyIterator
FilesystemIterator (5.3)
GlobIterator (5.3)
Unifying interfaces:
RecursiveIterator
SeekableIterator
OuterIterator

13.
More Iterators...
Many SPL data structures implement Iterator
-> They can be passed directly to decorators:
More iterators implemented in PHP in CVS:
ext/spl/examples/*.inc, *.php
For example: callbackFilterIterator.inc
Implementation of FilterIterator which uses a callback (or closure) as the filter function.
$s = new SplStack();
$i = new InfiniteIterator ( $s );
$s ->push( 1 ); $s ->push( 2 ); $s ->push( 3 );
foreach ( $i as $v ) {
echo &quot; $v &quot; ; //3 2 1 3 2 1 3 2 1 3 2...
}

14.
A Note on Recursive Iterators...
This doesn't work:
Try this instead:
RecursiveFilterIterator, RecursiveDirectoryIterator etc... implement recursive behaviour but do not exploit it .
-> Perhaps they should be called “recursible” iterators?
A RecursiveIteratorIterator wraps a “recursible” iterators and exploits its recursive behaviour.
$a = array ( 1 , 2 , array ( 3 , 4 ));
$i = new RecursiveArrayIterator( $a );
foreach ( $i as $v ) { echo &quot; $v &quot; ; } // 1 2 Array
$a = array ( 1 , 2 , array ( 3 , 4 ));
$i = new RecursiveArrayIterator( $a );
$i = new RecursiveIteratorIterator ( $i );
foreach ( $i as $v ) { echo &quot; $v &quot; ; } // 1 2 3 4

15.
SPL Iterators
Iterator decorators:
AppendIterator
CachingIterator
FilterIterator
InfiniteIterator
IteratorIterator
LimitIterator
MultipleIterator (5.3)
NoRewindIterator
ParentIterator
RegexIterator
RecursiveIteratorIterator
RecursiveCachingIterator
RecursiveFilterIterator
RecursiveRegexIterator
RecursiveTreeIterator (5.3)
Concrete iterators:
ArrayIterator
RecursiveArrayIterator
DirectoryIterator
RecursiveDirectoryIterator
EmptyIterator
FilesystemIterator (5.3)
GlobIterator (5.3)
Unifying interfaces:
RecursiveIterator
SeekableIterator
OuterIterator

16.
SPL Exceptions
SPL exceptions provide no extra logic or behaviour.
Each one is associated with a scenario by convention .
Extend them to specialize them for your domain .
Benefits:
-> Improve consistency of exception use within & across projects.
-> Increase the self-documenting nature of your code.

17.
More SPL Stuff...
Observer Pattern
Simple interfaces: SplObserver, SplSubject
Autoload Enhancements
Default autoloader with extension filtering
Define and chain custom autoload callbacks
Utility Functions
iterator_apply () , iterator_count () , iterator_to_array ()
class_implements () , class_parents ()
spl_object_hash ()

18.
Testing SPL
Great way to learn (more) about SPL !
See current code coverage :
http://gcov.php.net/PHP_5_3/lcov_html/spl
All tests are valuable!
Tests for basic functionality
Tests for interesting edge cases

19.
Come to TestFest!
Saturday 9 th May 2009 @ IBM SouthBank
Never used SPL? Come to learn!
Already know SPL? Come to to dig deeper!
Make PHP better!
Get kudos!
Win an elephpant!

20.
Iterators – bonus
What's this Traversable interface all about?
Iterator and IteratorAggregate both extend Traversable .
Traversable is a marker interface (it does not provide any methods).
It is used internally by the engine to detect iterability.
It cannot be implemented directly from PHP code – only indirectly, via Iterator and IteratorAggregate
But it can be implemented directly by internal classes to provide limited iterability, without implementing the full Iterator interface .
Few people need worry about it.