oktal3700

Guaranteed copy elision for named return values

This proposal aims to provide guaranteed copy elision for common cases of local variables being returned from a function.

Motivation

The accepted P0135 proposal already provides guaranteed copy elision for when a prvalue is returned from a function by stating that the result object of that prvalue (and not a temporary) is directly copy-initialized. It de-facto mandates what was known as Return Value Optimization (RVO) and allows non-movable objects to be returned in such a way.

Meanwhile, other cases of copy elision are still optional. For example, sometimes we want to create an object, set it up and return it.

psayre23

Below are the Big O performance of common functions of different Java Collections.


List                 | Add  | Remove | Get  | Contains | Next | Data Structure
---------------------|------|--------|------|----------|------|---------------
ArrayList            | O(1) |  O(n)  | O(1) |   O(n)   | O(1) | Array
LinkedList           | O(1) |  O(1)  | O(n) |   O(n)   | O(1) | Linked List
CopyOnWriteArrayList | O(n) |  O(n)  | O(1) |   O(n)   | O(1) | Array