Proposed modification to SE-0377: should explicit parameter ownership modifiers suppress implicit copying?

[Andrew_Trick]

@jrose

Is there consume var? Or are these always immutable? And borrow locals are as-of-yet unpitched, so I’m not sure how to think about how often I might want to copy them.

No, consume takes the place of var. As a local variable binding, we want it to to be assignable so that you don't need to lose control of ownership just to update a variable. The default assumption is that consume parameter binding is not assignable, but maybe that should change.

"borrow variables" were pitched here:

A roadmap for improving Swift performance predictability: ARC improvements and ownership control

Swift's high-level semantics try to relieve programmers from thinking about memory management in typical application code. In situations where predictable performance and runtime behavior are needed, though, the variability of ARC and Swift's optimizer have proven difficult for performance-oriented programmers to work with. The Swift Performance team at Apple are working on a series of language changes and features that will make the ARC model easier to understand, while also expanding the bread…