Synchronously (well) wait for async Task value update https://twitter.com/krzyzanowskim/status/1523233140914876416

AsyncWaiter.swift

/// Wait for async operation to return value and call callback with the value
/// This class is intended to workaround/simplify async/await + actors isolation
/// https://twitter.com/krzyzanowskim/status/1523233140914876416
private class AsyncWaiter<T> {
    var didReceiveValue: Bool = false
    let value: (T) -> Void
    let operation: () async throws -> T

    init(_ value: @escaping (T) -> Void, operation: @escaping () async throws -> T) {
        self.value = value
        self.operation = operation
    }

    func wait() {
        Task.detached {
            do {
                self.value(try await self.operation())
                self.signal()
            } catch {
                self.signal()
                throw error
            }
        }

        while !didReceiveValue {
            RunLoop.current.run(mode: .default, before: .distantFuture)
        }
    }

    func signal() {
        didReceiveValue = true
    }
}


extension Task where Success == Void, Failure == CancellationError {

    struct ValueError: LocalizedError {
        var errorDescription: String? {
            "Didn't receive asynchronous value."
        }
    }

    public static func wait<T>(operation: @escaping () async throws -> T) throws -> T {
        var v: T? = nil
        AsyncWaiter({
            v = $0
        }, operation: operation).wait()

        if let v = v {
            return v
        } else {
            throw ValueError()
        }
    }
}

example.swift

let result: [String] = try Task.wait {
    try await foo.getValues()
}

print(result)