[6.0] Alternative noncopyable switch design based on expression kind. #72954
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
If an expression refers to noncopyable storage, then default to performing a borrowing switch, where `let` bindings in patterns borrow out of the matched value. If an expression refers to a temporary value or explicitly uses the `consume` keyword, then perform a consuming switch, where `let` bindings take ownership of corresponding parts of the matched value. Allow `_borrowing` to still be used to explicitly bind a pattern variable as a borrow, with no-implicit-copy semantics for copyable values.
|
@swift-ci Please test |
kavon
approved these changes
Apr 10, 2024
|
@swift-ci Please test Linux |
tbkka
approved these changes
Apr 10, 2024
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Explanation: Pre-review discussion of the noncopyable borrowing switch feature raised a preference for an alternative design where the ownership of a switch is driven by what the expression refers to: If an expression refers to noncopyable storage, then default to performing a borrowing switch, where
letbindings in patterns borrow out of the matched value. If an expression refers to a temporary value or explicitly uses theconsumekeyword, then perform a consuming switch, whereletbindings take ownership of corresponding parts of the matched value. Allow_borrowingto still be used to explicitly bind a pattern variable as a borrow, with no-implicit-copy semantics for copyable values.Scope: Changes behavior of a pre-release experimental feature.
Issue: rdar://126212597
Original PR: #72647
Risk: Low. This should have no effect on code using released features only. For early adopters of the feature, the necessary source changes are also minimal; one only needs to explicitly write
switch consume xwhenxis a local variable binding that would otherwise be borrowed by default.Testing: Swift CI
Reviewer: @kavon