Editing Iterator (section)

==Implicit iterator==

Some object-oriented languages such as [[C Sharp (programming language)|C#]], [[C++]] (later versions), [[Object Pascal|Delphi]] (later versions), [[Go (programming language)|Go]], [[Java (programming language)|Java]] (later versions), [[Lua (programming language)|Lua]], [[Perl]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]] provide an [[Intrinsic function|intrinsic]] way of iterating through the elements of a collection without an explicit iterator. An iterator object may exist, but is not   represented in the source code.<ref name=ExternalInternal /><ref name="HFDPIterators">{{cite book
 | last1         = Freeman
 | first1        = Eric
 | last2         = Freeman
 | first2        = Elisabeth 
 | last3         = Kathy
 | first3        = Sierra
 | last4         = Bert
 | first4        = Bates
 | editor-last   = Hendrickson
 | editor-first  = Mike
 | editor2-last  = Loukides
 | editor2-first = Mike
 | year          = 2004
 | title         = Head First Design Patterns
 | volume        = 1
 | pages         = 338
 | publisher     = O'REILLY
 | format        = paperback
 | isbn          = 978-0-596-00712-6
 | access-date    = 2012-08-09
 | url           = http://shop.oreilly.com/product/9780596007126.do
}}</ref>

An implicit iterator is often manifest in language syntax as <code>[[foreach]]</code>.

In Python, a collection object can be iterated directly:

<syntaxhighlight lang="python">
for value in iterable:
    print(value)
</syntaxhighlight>

In Ruby, iteration requires accessing an iterator property:

<syntaxhighlight lang="ruby">
iterable.each do |value|
  puts value
end
</syntaxhighlight>

This iteration style is sometimes called "internal iteration" because its code fully executes within the context of the iterable object (that controls all aspects of iteration), and the programmer only provides the operation to execute at each step (using an [[anonymous function]]).

Languages that support [[list comprehension]]s or similar constructs may also make use of implicit iterators during the construction of the result list, as in Python:

<syntaxhighlight lang="python">
names = [person.name for person in roster if person.male]
</syntaxhighlight>

Sometimes the implicit hidden nature is only partial. The [[C++]] language has a few function templates for implicit iteration, such as <code>for_each()</code>. These functions still require explicit iterator objects as their initial input, but the subsequent iteration does not expose an iterator object to the user.