Editing In-place algorithm (section)

== In functional programming ==
{{See also|Purely functional data structure}}
[[Functional programming]] languages often discourage or do not support explicit in-place algorithms that overwrite data, since this is a type of [[side effect (computer science)|side effect]]; instead, they only allow new data to be constructed. However, good functional language compilers will often recognize when an object very similar to an existing one is created and then the old one is thrown away, and will optimize this into a simple mutation "under the hood".

Note that it is possible in principle to carefully construct in-place algorithms that do not modify data (unless the data is no longer being used), but this is rarely done in practice.