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 .

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Why use SPL?
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Zend
Framework

Agavi

SPL Documentation
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SPL Data Structures
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Iterators
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An iterator implements a consistent interface for traversing a collection .
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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
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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:

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- 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...
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$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...
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$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 Exceptions

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Benefits:
-> Improve consistency of exception use within & across projects.

-> Increase the self-documenting nature of your code.

More SPL Stuff...
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Testing SPL
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Come to TestFest!
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Iterators – bonus
What's this Traversable interface all about?
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An Introduction to SPL, the Standard PHP Library

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