For what type of data or scenarios is the copy-on-write technique used?

Copy-on-write (COW) technique is used to optimize handling data that is frequently copied but rarely modified. Instead of immediately creating a full copy of an object, the system shares one copy among multiple owners and creates a real copy only when someone attempts to modify the data.

In iOS, copy-on-write is applied, for example, in data structures such as Array, Dictionary, and String. This allows for efficient memory usage and improves performance when passing and copying large amounts of data.

Example: if you have an array that you pass to a function, a copy is not actually created until the function tries to modify the array. Then, a new copy is made, and the changes are applied to it.