Editing Persistent data structure (section)

=== Copy-on-write ===
One method for creating a persistent data structure is to use a platform provided ephemeral data structure such as an [[Mutable array|array]] to store the data in the data structure and copy the entirety of that data structure using [[Copy-on-write|copy-on-write semantics]] for any updates to the data structure. This is an inefficient technique because the entire backing data structure must be copied for each write, leading to worst case O(n·m) performance characteristics for m modifications of an array of size n.{{citation needed|date=May 2019}}