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[SE-0494] small trivially identical updates #3029

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44 changes: 26 additions & 18 deletions proposals/0494-add-is-identical-methods.md
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Expand Up @@ -4,7 +4,7 @@
* Authors: [Rick van Voorden](https://github.com/vanvoorden), [Karoy Lorentey](https://github.com/lorentey)
* Review Manager: [John McCall](https://github.com/rjmccall)
* Status: **Accepted with modifications**
* Implementation: ([String, Substring](https://github.com/swiftlang/swift/pull/82055)), ([Array, ArraySlice, ContiguousArray](https://github.com/swiftlang/swift/pull/82438)), ([Dictionary, Set](https://github.com/swiftlang/swift/pull/82439))
* Implementation: [swift/issues/84991](https://github.com/swiftlang/swift/issues/84991)
* Review: ([prepitch](https://forums.swift.org/t/-/78792)) ([first pitch](https://forums.swift.org/t/-/79145)) ([second pitch](https://forums.swift.org/t/-/80496)) ([review](https://forums.swift.org/t/se-0494-add-isidentical-to-methods-for-quick-comparisons-to-concrete-types/82296)) ([revision](https://forums.swift.org/t/se-0494-add-isidentical-to-methods-for-quick-comparisons-to-concrete-types/82296/142)) ([acceptance](https://forums.swift.org/t/accepted-with-modifications-se-0494-add-isidentical-to-methods-for-quick-comparison-to-concrete-types/82695))

### Table of Contents
Expand Down Expand Up @@ -301,6 +301,7 @@ Many more examples of `isIdentical(to:)` functions are currently shipping in `Sw
Before we look at the concrete types in this proposal, let’s begin with some more general principles and ideas we would expect for *all* concrete types to follow when adopting this new method. While this specific proposal is not adding a new protocol to Standard Library, it could be helpful to think of an “informal” protocol that guides us in choosing the types to adopt this new method. This could then serve as a guide for library maintainers that might choose to adopt this method on *new* types in the future.

Suppose we are proposing an `isTriviallyIdentical(to:)` method on a type `T`. We propose the following axioms that library maintainers should adopt:

* `a.isTriviallyIdentical(to: a)` is always `true` (Reflexivity)
* If `T` is `Equatable`:
* `a.isTriviallyIdentical(to: b)` implies `a == b` (*or else `a` and `b` are exceptional values*)
Expand Down Expand Up @@ -394,6 +395,7 @@ When we build and run our SwiftUI app we confirm that we are not computing new `
## Detailed Design

We propose adding `isTriviallyIdentical(to:)` methods to the following concrete types from Standard Library:

* `String`
* `String.UnicodeScalarView`
* `String.UTF16View`
Expand Down Expand Up @@ -453,6 +455,7 @@ extension String {
```

The following types will adopt `isTriviallyIdentical(to:)` with the same semantic guarantees as `String`:

* `String.UnicodeScalarView`
* `String.UTF16View`
* `String.UTF8View`
Expand Down Expand Up @@ -493,6 +496,7 @@ extension Substring {
```

The following types will adopt `isTriviallyIdentical(to:)` with the same semantic guarantees as `Substring`:

* `Substring.UnicodeScalarView`
* `Substring.UTF16View`
* `Substring.UTF8View`
Expand Down Expand Up @@ -616,6 +620,7 @@ extension UnsafeBufferPointer where Element: ~Copyable {
```

The following types will adopt `isTriviallyIdentical(to:)` with the same semantic guarantees as `UnsafeBufferPointer`:

* `UnsafeMutableBufferPointer`
* `UnsafeMutableRawBufferPointer`
* `UnsafeRawBufferPointer`
Expand Down Expand Up @@ -651,7 +656,6 @@ Any Standard Library types that are copy-on-write values could be good candidate
* `KeyValuePairs`
* `StaticBigInt`
* `StaticString`
* `UTF8Span`

This proposal focuses on what we see as the most high-impact types to support from Standard Library. This proposal *is not* meant to discourage adding `isTriviallyIdentical(to:)` on any of these types at some point in the future. A follow-up “second-round” proposal could focus on these remaining types.

Expand Down Expand Up @@ -719,19 +723,23 @@ Thanks to [Xiaodi Wu](https://forums.swift.org/t/-/80496/67) for proposing that

Thanks to [QuinceyMorris](https://forums.swift.org/t/-/82296/72) for proposing the name `isTriviallyIdentical(to:)`.

[^1]: https://github.com/swiftlang/swift/blob/swift-6.1.2-RELEASE/stdlib/public/core/String.swift#L397-L415
[^2]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/DequeModule/Deque._Storage.swift#L223-L225
[^3]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/HashTreeCollections/HashNode/_HashNode.swift#L78-L80
[^4]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/HashTreeCollections/HashNode/_RawHashNode.swift#L50-L52
[^5]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Conformances/BigString%2BEquatable.swift#L14-L16
[^6]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigString%2BUnicodeScalarView.swift#L77-L79
[^7]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigString%2BUTF8View.swift#L39-L41
[^8]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigString%2BUTF16View.swift#L39-L41
[^9]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring.swift#L100-L103
[^10]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring%2BUnicodeScalarView.swift#L94-L97
[^11]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring%2BUTF8View.swift#L64-L67
[^12]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring%2BUTF16View.swift#L87-L90
[^13]: https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/Rope/Basics/Rope.swift#L68-L70
[^14]: https://github.com/swiftlang/swift-markdown/blob/swift-6.1.1-RELEASE/Sources/Markdown/Base/Markup.swift#L370-L372
[^15]: https://github.com/Swift-CowBox/Swift-CowBox/blob/1.1.0/Sources/CowBox/CowBox.swift#L19-L27
[^16]: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0447-span-access-shared-contiguous-storage.md
Thanks to [benrimmington](https://github.com/swiftlang/swift/pull/84998) for volunteering to contribute implementations.

Thanks to [WindowsMEMZ](https://github.com/swiftlang/swift/pull/85171) for volunteering to contribute implementations.

[^1]: <https://github.com/swiftlang/swift/blob/swift-6.1.2-RELEASE/stdlib/public/core/String.swift#L397-L415>
[^2]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/DequeModule/Deque._Storage.swift#L223-L225>
[^3]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/HashTreeCollections/HashNode/_HashNode.swift#L78-L80>
[^4]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/HashTreeCollections/HashNode/_RawHashNode.swift#L50-L52>
[^5]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Conformances/BigString%2BEquatable.swift#L14-L16>
[^6]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigString%2BUnicodeScalarView.swift#L77-L79>
[^7]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigString%2BUTF8View.swift#L39-L41>
[^8]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigString%2BUTF16View.swift#L39-L41>
[^9]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring.swift#L100-L103>
[^10]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring%2BUnicodeScalarView.swift#L94-L97>
[^11]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring%2BUTF8View.swift#L64-L67>
[^12]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/BigString/Views/BigSubstring%2BUTF16View.swift#L87-L90>
[^13]: <https://github.com/apple/swift-collections/blob/1.2.0/Sources/RopeModule/Rope/Basics/Rope.swift#L68-L70>
[^14]: <https://github.com/swiftlang/swift-markdown/blob/swift-6.1.1-RELEASE/Sources/Markdown/Base/Markup.swift#L370-L372>
[^15]: <https://github.com/Swift-CowBox/Swift-CowBox/blob/1.1.0/Sources/CowBox/CowBox.swift#L19-L27>
[^16]: <https://github.com/swiftlang/swift-evolution/blob/main/proposals/0447-span-access-shared-contiguous-storage.md>