Question

I want to write an asynchronous function that accepts a closure with handlers like HTTPBuilder.request does. How is the function written?

When I call the function, it will look like this:

// calling my function now - we'll process the results when status is available...
myFunction(arg1, arg2) {
  status.success = { result ->
    println 'cool'
  }
  status.failure = { result ->
    println 'not cool'
  }
}

Answer 1

The “body” of myFunction is actually a third parameter of type Closure. When you declare it, it will actually have three parameters: arg1, arg2, and one more containing the body.

In myFunction call the body closure with a delegate. The delegate holds the status.success and status.failure event handler closures. Then do your async operation and capture the result. Finally, invoke the appropriate result handler closure. The skeleton for a function like this would look something like this:

def myFunction(arg1, arg2, Closure body) {
    def delegateMap = [status:[:]]
    body.delegate = delegateMap
    body.call()

    // start async process
    Thread.start {
         def result = doAsyncStuff()
         if (isSuccess(result) && delegateMap.status.success) {
             delegateMap.status.success.call(result)
         }
         else if (isFailure(result) && delegateMap.status.failure) {
             delegateMap.status.failure.call(result)
         }
    }
}