1. An Introduction to SPL, the Standard PHP Library
Robin Fernandes ( )

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)

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

5. SPL Data Structures In PHP 5.2: New in PHP 5.3:
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 ... ... ... ... ... ... ... ... Collections: Class
MyList
Class
MyGraph
Class
MyStruct1
???
Class
MyStruct2
???
... 1 4 5 3 2 1 2 3 4
Algorithms:
...
function
showList()
function
showGraph()
function
showS1()
function
showS2()
Display:
function
sumList()
function
sumGraph()
function
sumS1()
function
sumS2()
...
Sum:
function
avgList()
function
avgGraph()
function
avgS1()
function
avgS2()
...
Average:
...
...
...
...

8. With Iterators ... ... Algorithms are decoupled from collections!
Class
MyList
Class
MyGraph
Class
MyStruct1
???
Class
MyStruct2
??? 1 4 5 3 2 1 2 3 4
...
Iterators:
Class
MyList
Iterator
Class
MyGraph
Iterator
Class
MyStruct1
Iterator
Class
MyStruct2
Iterator
function
show()
Algorithms:
function
sum()
Algorithms are
decoupled
from collections!
function
avg()
...

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 $node) {
echo "$node<br/>"; }
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 }
… is equivalent to ...
// 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();
Note:
- User-space classes can't implement Traversable directly.
- No class can implement both Iterator and IteratorAggregate.
<=>

12. SPL Iterators Concrete iterators: ArrayIterator RecursiveArrayIterator
DirectoryIterator
RecursiveDirectoryIterator
EmptyIterator
FilesystemIterator (5.3)
GlobIterator (5.3)
Iterator decorators:
AppendIterator
CachingIterator
FilterIterator
InfiniteIterator
IteratorIterator
LimitIterator
MultipleIterator (5.3)
NoRewindIterator
ParentIterator
RegexIterator
RecursiveIteratorIterator
RecursiveCachingIterator
RecursiveFilterIterator
RecursiveRegexIterator
RecursiveTreeIterator (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 $v) {
echo "$v "; // }

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 $v) { echo "$v "; } // 1 2 Array
$a = array(1, 2, array(3, 4));
$i = new RecursiveArrayIterator($a);
$i = new RecursiveIteratorIterator($i);
foreach ($i as $v) { echo "$v "; } //

15. SPL Iterators Concrete iterators: ArrayIterator RecursiveArrayIterator
DirectoryIterator
RecursiveDirectoryIterator
EmptyIterator
FilesystemIterator (5.3)
GlobIterator (5.3)
Iterator decorators:
AppendIterator
CachingIterator
FilterIterator
InfiniteIterator
IteratorIterator
LimitIterator
MultipleIterator (5.3)
NoRewindIterator
ParentIterator
RegexIterator
RecursiveIteratorIterator
RecursiveCachingIterator
RecursiveFilterIterator
RecursiveRegexIterator
RecursiveTreeIterator (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. Simple interfaces: SplObserver, SplSubject
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:
All tests are valuable!
Tests for basic functionality
Tests for interesting edge cases

19. Come to TestFest! Saturday 9th 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.