How to wait for a closure completion before returning a value

Question

How to wait to return a value after a closure completion.

Example:

func testmethod() -> String {
   var abc = ""
   /* some asynchronous service call block that sets abc to some other value */ {
      abc = "xyz"
   }
   return abc 
}

Now I want the method to return only after xyz value has been set for variable and not empty string.

How to achieve this?

Answer 1

It is possible (However make sure this is what you really want.).

You have to use something that will block a thread until a resource is available, like semaphores.

var foo: String {
    let semaphore = DispatchSemaphore(value: 0)
    var string = ""

    getSomethingAsynchronously { something in
        string = something
        semaphore.signal()
    }

    semaphore.wait()
    return string
}

Bare in mind that the thread you are working on will be blocked until the getSomethingAsynchronously is done.