A sample using a closure for asynchronous tasks

completionAsynchronousSample.swift

func useAsynchronousFetch() -> Void {
    fetchData(value: 23) { result in
        switch result {
            case .success(let data):
                transformData(data) { result in
                    switch result {
                        case .success(let viewModel):
                            displayModel(viewModel)
                        case .failure(let error):
                            displayError(error)
                    }
                }
            case .failure(let error):
                displayError(error)
        }
    }
}