Lifetime Dependency Annotations for Non-escapable Types #2305

tbkka · 2024-02-05T22:14:10Z

This is a companion proposal to "Non-Escapable Types".

It proposes a set of annotations that can be used to relate the lifetimes of two objects. For example, this can be used to ensure that a "slice" or "iterator" object that holds a pointer into some container does not outlive the container.

…rences

proposals/NNNN-lifetime-dependency.md

tbkka · 2024-03-21T15:52:35Z

Overhauled to reflect a fundamentally different syntax. We now have a single @dependsOn(arg) marker that simply states the fact of the dependency rather than a set of borrow/mutate/consume/copy markers that state the type. This follows from conversation about the previous proposal: Since there is almost always only one type of dependency possible for any given function signature, we can simplify the syntax. This should also help users of libraries that expose nonescapable types: those users only need to know what values have dependencies; they generally do not need to be aware of the precise semantics underlying that dependency.

proposals/NNNN-lifetime-dependency.md

Pitch - apple/swift-evolution#2305

@dependsOn

… pitch Pitch - apple/swift-evolution#2305 Changes highlights: @dependsOn(paramName) and @dependsOn(scoped argName) syntax @dependsOn(paramName) -> copy lifetime dependence for all parameters/self except when we have Escapable parameters/self, we assign scope lifetime dependence. Allow lifetime dependence on parameters without ownership modifier. Always infer copy lifetime dependence except when we have Escapable parameters/self, we infer scope lifetime dependence. Allow lifetime dependence inference on parameters without ownership modifier.

@dependsOn

… pitch Pitch - apple/swift-evolution#2305 Changes highlights: @dependsOn(paramName) and @dependsOn(scoped argName) syntax @dependsOn(paramName) -> copy lifetime dependence for all parameters/self except when we have Escapable parameters/self, we assign scope lifetime dependence. Allow lifetime dependence on parameters without ownership modifier. Always infer copy lifetime dependence except when we have Escapable parameters/self, we infer scope lifetime dependence. Allow lifetime dependence inference on parameters without ownership modifier.

We need to separate description of the dependency itself -- which places a bound on when particular objects can be destroyed -- from the syntax. In particular, the syntax specifies a relationship between two objects, but that relationship is not always a lifetime dependency itself (because of "copied" dependencies).

… pitch Pitch - apple/swift-evolution#2305 Changes highlights: dependsOn(paramName) and dependsOn(scoped argName) syntax dependsOn(paramName) -> copy lifetime dependence for all parameters/self except when we have Escapable parameters/self, we assign scope lifetime dependence. Allow lifetime dependence on parameters without ownership modifier. Always infer copy lifetime dependence except when we have Escapable parameters/self, we infer scope lifetime dependence. Allow lifetime dependence inference on parameters without ownership modifier.

Also, fix the proposed syntax for properties

lorentey · 2024-05-01T18:42:36Z

proposals/NNNN-lifetime-dependency.md

+These would also be useable with methods that wish to declare a dependency on `self`.
+To reduce the burden of manually adding such annotations, we also propose inferring lifetime dependencies in certain common cases without requiring any additional annotations.
+
+This is a key requirement for the `StorageView` type (previously called `BufferView`) being discussed elsewhere, and is closely related to the proposal for `~Escapable` types.


We have named this construct Span. Please let's avoid mentioning its deadnames; proposals are forever, and we really need to avoid indefinitely propagating these obsolete names.

Suggested change

This is a key requirement for the `StorageView` type (previously called `BufferView`) being discussed elsewhere, and is closely related to the proposal for `~Escapable` types.

This is a key requirement for the `Span` type that is being discussed elsewhere, and is closely related to the proposal for `~Escapable` types.

…bling proposal.

Changed `StorageView` and `BufferReference` to `Span` to match the si…

tbkka added 4 commits January 24, 2024 18:16

First full draft.

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Whitespace cleanup

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Fix formatting

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Future direction: Lifetime dependencies between arguments

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tbkka changed the title ~~Tbkka lifetime dependency~~ Lifetime Dependency Annotations for Non-escapable Types Feb 5, 2024

tbkka mentioned this pull request Feb 5, 2024

Non-Escapable Types #2304

Open

Link to pitch thread

2992389

glessard mentioned this pull request Feb 6, 2024

Safe Access to Contiguous Storage #2307

Open

tbkka added 5 commits February 7, 2024 15:41

New examples for Future Directions

ba3946c

Match the implementation: Use local parameter names for argument refe…

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…rences

Clarify some Alternatives and Future Directions

f9b06b7

methods are mutating, not inout

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Expand alternative syntaxes

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meg-gupta reviewed Mar 20, 2024

View reviewed changes

Overhaul to adopt the new @dependsOn() syntax

78d07f2