Iterator pattern
From Wikipedia, the free encyclopedia
In object-oriented programming, the Iterator pattern is a design pattern in which iterators are used to access the elements of an aggregate object sequentially without exposing its underlying representation. An Iterator object encapsulates the internal structure of how the iteration occurs.
For example, a tree, linked list, hash table, and an array all need to be iterated with Search, Sort, Next. Rather than having 12 different methods to manage, using this Pattern would allow you to only need to manage 7 methods.
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[edit] Examples
[edit] PHP 5
As a default behavior in PHP 5, using an object in a foreach structure will traverse all public values. Multiple Iterator classes are available with PHP to allow you to iterate through common lists, such as directories, XML structures and recursive arrays.
It's possible to define your own Iterator classes by implementing the Iterator interface, which will override the default behavior.
The Iterator interface definition:
interface Iterator
{
// Returns the current value
function current();
// Returns the current key
function key();
// Moves the internal pointer to the next element
function next();
// Moves the internal pointer to the first element
function rewind();
// If the current element is valid (boolean)
function valid();
}
These methods are all being used in a complete foreach( $object as $key=>$value ) sequence. The methods are executed in the following order:
rewind()
if valid() {
current() in $value
key() in $key
next()
}
End of Loop
According to Zend, the current() method is called before and after the valid() method
[edit] See also
[edit] External links
- Object iteration in PHP
Creational: Abstract factory • Builder • Factory • Prototype • Singleton
Structural: Adapter • Bridge • Composite • Decorator • Façade • Flyweight • Proxy
Behavorial: Chain of responsibility • Command • Interpreter • Iterator • Mediator • Memento • Observer • State • Strategy • Template method • Visitor
