# SE-0360: Opaque result types with limited availability

**URL:** <https://forums.swift.org/t/se-0360-opaque-result-types-with-limited-availability/57729>\
**Category:** Proposal Reviews\
**Created:** [May 31, 2022, 6:58pm UTC](https://forums.swift.org/t/se-0360-opaque-result-types-with-limited-availability/57729 "2022-05-31T18:58:24Z")\
**Posts on this page:** 1\
**Showing post:** 12

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**Author:** ![pyrtsa](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/pyrtsa/32/740_2.png) [@pyrtsa](https://forums.swift.org/u/pyrtsa)\
**Post date:** [June 2, 2022, 1:05pm UTC](https://forums.swift.org/t/se-0360-opaque-result-types-with-limited-availability/57729/12 "2022-06-02T13:05:25Z")

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The example demonstrated by the proposal does not make it particularly clear, but this seems like a useful feature towards making APIs back-portable by 1st or 3rd parties. 🎉

For a trivial example, I could think of ways to make SwiftUI’s [`refreshable(action:)`](https://developer.apple.com/documentation/swiftui/view/refreshable(action:)) modifier available (albeit in a renamed form\[1\]) to older platform versions without resorting to `SwiftUI._ConditionalContent` the actual return type of the modifier:

```swift
extension View {
    // Note: no `@ViewBuilder` here!
    @available(iOS 14.0, *)
    func refreshable_(action: @escaping @Sendable () async -> Void) -> some View {
        if #available(iOS 15.0, *) {
            return self.refreshable(action: action)
        }
        // Something like https://github.com/siteline/SwiftUI-Introspect#scrollview
        ...
    }
}

```

(If the function interface to backport contains data types or protocols unavailable to older targeted platform versions, however, then I'm afraid something more is needed than this proposal alone.)

* * *

> - What is your evaluation of the proposal?

+1

> - Is the problem being addressed significant enough to warrant a change to Swift?

Yes.

> - Does this proposal fit well with the feel and direction of Swift?

It seems like a natural extension to the rules about `#available` (and `#unavailable`).

> - If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?

N/A

> - How much effort did you put into your review? A glance, a quick reading, or an in-depth study?

Quick reading, but also gave it a quick try on the latest `main` snapshot toolchain using iOS Simulator 14.5 and 15.5.

* * *

1. Completely shadowing the existing implementation would further need a way for the shadowing function’s body to refer back to the shadowed one in the `SwiftUI` module in a qualified form, say, `return `SwiftUI.View`.refreshable(action: action)`. Something similar was discussed but mainly for module-level symbols, not members, in [Pitch: Fully qualified name syntax](https://forums.swift.org/t/pitch-fully-qualified-name-syntax/28482).

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