Swift Pitch: “borrow” and “take” Parameter Ownership Modifiers
We propose new
borrowandtakeparameter modifiers to allow developers to explicitly choose the ownership convention that a function uses to receive immutable parameters. This allows for fine-tuning of performance by reducing the number of ARC calls or copies needed to call a function, and provides a necessary prerequisite feature for move-only types to specify whether a function consumes a move-only value or not.[…]
Looking to the future, as part of our ongoing project to add ownership to Swift, we will eventually have move-only values and types. Since move-only types do not have the ability to be copied, the distinction between the two conventions becomes an important part of the API contract: functions that borrow move-only values make temporary use of the value and leave it valid for further use, like reading from a file handle, whereas functions that take a move-only value consume it and prevent its further use, like closing a file handle. Relying on implicit selection of the parameter convention will not suffice for these types.
Previously:
- Swift Proposal: Move Function
- Roadmap for Improving Swift Performance Predictability
- Swift Ownership Manifesto
