Storing closures and NonIsolatedNonSending

Using Swift
1

The following code compiles fine without NonIsolatedNonSendingByDefault

protocol Writer {}

public struct Response: Sendable {
    let write: @Sendable (inout any Writer) async throws -> Void

    init(_ write: @Sendable @escaping (inout any Writer) async throws -> Void) {
        self.write = { writer in
            try await write(&writer)
        }
    }
}

When I enable `NonIsolatedNonSendingByDefault` I get the following error

Cannot convert '@Sendable (inout any Writer) async throws -> Void' to 'nonisolated(nonsending) @Sendable (inout any Writer) async throws -> Void' because crossing of an isolation boundary requires parameter and result types to conform to 'Sendable' protocol

It appears to be related to the closure as I can replace the closure with self.write = write and everything works.

In fact if I replace the closure with self.write = { _ in } I get the error again.

Is this expected? And if so is there a way around this?

2

Ok I can work around this by adding @concurrent to the declaration of the write member variable.

This makes that part of the code compile, but now my function is tagged as @concurrent which I’d prefer it wasn’t.