Editing Visitor pattern (section)

=== Iteration loops ===
{{See also|Iterator pattern}}
The visitor pattern may be used for iteration over [[Container (abstract data type)|container]]-like data structures just like [[Iterator pattern]] but with limited functionality.<ref name="Budd1997">{{Cite book |last=Budd |first=Timothy |url=https://www.worldcat.org/oclc/34788238 |title=An introduction to object-oriented programming |date=1997 |publisher=Addison-Wesley |isbn=0-201-82419-1 |edition=2nd |location=Reading, Mass. |oclc=34788238}}</ref>{{Rp|page=288}} For example, [[iteration]] over a directory structure could be implemented by a function class<!-- <- this is not a mistake, it means class Function {...} --> instead of more conventional [[Loop (programming)|loop pattern]]. This would allow deriving various useful information from directories content by implementing a visitor functionality for every item while [[Code reuse|reusing]] the iteration code. It's widely employed in Smalltalk systems and can be found in C++ as well.{{r|Budd1997|p=289}} A drawback of this approach, however, is that you can't break out of the loop easily or iterate concurrently (in parallel i.e. traversing two containers at the same time by a single {{Code|i}} variable).{{r|Budd1997|p=289}} The latter would require writing additional functionality for a visitor to support these features.{{r|Budd1997|p=289}}