How does this example using Span and Swift concurrency compiles?

Using Swift
9

I'm not sure RBI can entirely fix this issue. E.g. you have a sort of worse problem than the fully synchronous case if you involve multiple tasks, even if they are all serialized with the same isolation:

// run this with ASAN on and you see use after frees and no dynamic exclusivity trap

@MainActor
func testSpan() async throws {
    var array: [Double] = [1, 2, 3]
    let span = array.span

    await Task { @MainActor in
        array.append(4)
    }.value

    for i in span.indices {
        print(span[i])
    }
}

try await testSpan()
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