Swift async method call for a command line app

Question

I'm trying to reuse some async marked code that works great in a SwiftUI application in a simple Swift-Command line tool. Lets assume for simplicity that I'd like to reuse a function

func fetchData(base : String) async throws -> SomeDate
    {
        let request = createURLRequest(forBase: base)
        
        let (data, response) = try await URLSession.shared.data(for: request)
        guard (response as? HTTPURLResponse)?.statusCode == 200 else {
            throw FetchError.urlResponse
        }
        let returnData = try! JSONDecoder().decode(SomeData.self, from: data)
        
        return returnData
    }

in my command line application. A call like

    let allInfo = try clerk.fetchData("base")

in my "main-function" gives the error message 'async' call in a function that does not support concurrency. What is the correct way to handle this case.

Thanks Patrick

Answer 1

To call an async method the call must take place inside an async method or wrapped in a Task.
Further the method must be called wirh await

Task {
    do {
        let allInfo = try await clerk.fetchData("base")
    } catch {
        print(error)
    }
}

You can make the entry point of the CLI async with this syntax

@main
struct CLI {
    static func main() async throws {

        let args = CommandLine.arguments
        ...
}

The name of the struct is arbitrary.

You need to rename the file from main.swift to CLI.swift to fix the error 'main' attribute cannot be used in a module that contains top-level code.