The An Iterator Pattern is commonly used in Computer Science as provides the user with a way to access the elements of a collectionsome kind of list sequentially, regardless while keeping the elements of how they were implemented. An iterator may also be called a cursorthat list from exposing their underlying representation.__TOC__=== Description ===An iterator may be though of as a kind of pointer that has two basic operations, referencing one particular element in a collection, and pointing to the next element in the collection. Depending on the language the iterator is implemented in, other functionality may be added to the iterator object.

The purpose of an iterator is == Introduction to give a user a way to process each element of a container while separating the user from the internal structure of the container. This allows the container to store elements however it wants to, while allowing the user to use it as if it were just a simple list or sequence. An iterator class is usually designed in coordination with the container class, which usually provides methods or functions for creating iterators.Iterators ==

An easy way iterator may be though of as a kind of pointer that has two basic operations, referencing one particular element in a collection, and pointing to think of iteratorsthe next element in the collection (current, and current.next). Depending on the language the iterator is implemented in, other functionality may be added to look at Linked Liststhe iterator object, because they operate very similarlysuch as remove and update and so on.

Iterator ties together the [http://en.wikipedia.org/wiki/Object_oriented_programming object-oriented programming] principles known as encapsulation and [http://en.wikipedia.org/wiki/Polymorphism_%28computer_science%29 polymorphism]. Using an iterator, you can manipulate the objects in a collection without explicitly knowing how the collection is implemented or what the collection is made up of (Different types of objects perhaps?). An iterator provides an interface to different iteration implementations, which contain the details of how to manipulate a specific collection, including which items in the collection to show (filtering) and in what order (sorting). An easy way to think of iterators, is to also think of, [http://en.wikipedia.org/wiki/List_%28computing%29 Lists], [http://en.wikipedia.org/wiki/Linked_list Linked Lists], [http://en.wikipedia.org/wiki/Binary_tree Binary Trees], and [http://en.wikipedia.org/wiki/Hash_tables Hash Tables], because they operate very much in the same way that iterators do.   === Implicit Iterators === Some object-oriented languages have iterator support included within the language, without having to implement an explicit iterator object. Some of these language include: * C#* Java (After 5.0)* Python* PERL  === UML === Design class diagram in UML of the Iterator Pattern being used in a system. [[Image:Iterator1.png]]  == Code Samples == The following are samples of code from C#, Java, Python, and PERL, displaying how they use their implicit iterators.  === C# ===  // C#, implicit iteration foreach (Value v in list) Console.WriteLine(v);  === Java ===  // Java, J2SE 5.0, implicit iteration for (Value v : list) System.out.print(v);  === Python ===  # Python, implicit iteration for Value in List: print Value  === PERL ===  # Perl, implicit iteration foreach $val (@list) { print "$val\n"; } == Examples == === C++ === This is a code snippet from a file called [http://www.google.com/codesearch?hl=en&q=show:3faa7gjspWs:MYoIVGFTT9Q:S6XmQxn_Gd8&sa=N&ct=rd&cs_p=http://gentoo.osuosl.org/distfiles/gnome-vfsmm-1.3.5.tar.gz&cs_f=gnome-vfsmm-1.3.5/libgnomevfs/libgnomevfsmm/transfer.cc transfer.cc], created by the Gnome VFS Development Team. This particular function, transfer_list, transfers a list of URI's from the source list to the target list. The source code repository can be found [http://www.google.com/codesearch?hl=en&q=show:7egWPqDRuQg:6mN6dZ6BKgU&sa=N&ct=rdp&cs_p=http://gentoo.osuosl.org/distfiles/gnome-vfsmm-1.3.5.tar.gz here].  void transfer_list(const Glib::StringArrayHandle& source_uri_list, const Glib::StringArrayHandle& target_uri_list, TransferOptions options, ErrorMode error_mode, OverwriteMode overwrite_mode, const SlotProgress& slot) { typedef std::list< Glib::RefPtr<Uri> > uri_list; uri_list sources, targets; //Build lists of RefPtr<Uri>s from the strings: Glib::StringArrayHandle::const_iterator iter_target = target_uri_list.begin(); for(Glib::StringArrayHandle::const_iterator iter = source_uri_list.begin(); iter != source_uri_list.end(); ++iter) { if(iter_target != target_uri_list.end()) { sources.push_back( Uri::create(*iter) ); targets.push_back( Uri::create(*iter_target) ); iter_target++; } } transfer_list_uris(sources, targets, options, error_mode, overwrite_mode, slot); }   == References == * [http://en.wikipedia.org/wiki/Iterator Wikipedia entry on Iterator]* [http://thor.info.uaic.ro/ Universitatea Alexandru Ioan Cuza]* [http://www.google.com/codesearch?hl=en&q=show:7egWPqDRuQg:6mN6dZ6BKgU&sa=N&ct=rdp&cs_p=http://gentoo.osuosl.org/distfiles/gnome-vfsmm-1.3.5.tar.gz Gnome VFS Development Source Code]