An Introduction to SPL, the Standard PHP Library

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

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...

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

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

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

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.

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

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

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(); }

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);

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.

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

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 " ; //3 2 1 3 2 1 3 2 1 3 2... }

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 " ; } // 1 2 3 4

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

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.

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 ()

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

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!

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.

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An Introduction to SPL, the Standard PHP Library

by Robin Fernandes

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