Introduction to Move-Only Types in Swift
I thought it would help to have an informal sketch to help outline why move-only types are interesting, clarify a few subtle points (like what “move” really means), and briefly explain some of the issues we’ll need to tackle in order to bring this to Swift.
[…]
So the first step in bringing move-only support to Swift is to add operations with different lifetime-management behaviors. This will include constructs such as
for borrow x in collectionthat let you iterate over the items in a collection without requiring an implicit copy andf(take x)that explicitly invalidates the local value as part of passing it into a function. We’re also exploring variations of these that would allow you to temporarily gain mutable access to a value. These would allow you to efficiently mutate an element “in place” in various scenarios, which is a useful optimization tool for copyable values and an essential prerequisite for move-only values.[…]
By making
Anya synonym forany Copyable, we can ensure thatAnyis itself always copyable at the cost of limiting it to only store copyable values. This redefinition would preserve the behavior of current code that usesAny. Of course, this means we need to introduce a new type that can hold any value whether it is copyable or not.
Previously:
- Swift Pitch: “borrow” and “take” Parameter Ownership Modifiers
- Swift Proposal: Move Function
- Roadmap for Improving Swift Performance Predictability
- On the Road to Swift 6
- Swift Ownership Manifesto
