Swift access closure members programmatically

Question

I am building a Swift app and using PromiseKit to make the async features more readable.

From the PromiseKit docs, I can see that it supports multiple concurrent promises. I wrote some code as follows to generate promises in a for loop then wait for them all to get fulfilled.

for index in 0...100 {
    let urlString = "https://someurl.com/item/\(index)"
    guard let url = URL(string: urlString) else { return }
    requestPromises += [URLSession.shared.dataTask(.promise, with: url).validate()]
}

firstly {
    when(fulfilled: requestPromises)
}.done {
    // process results
}

The example in the docs shows to write the promise as:

firstly {
    when(fulfilled: operation1(), operation2())
}.done { result1, result2 in
    //…
}

My problem is I don't want to write out result1, result2, ... result100. Is there a way to programmatically access the results?

I had a quick run through the extend docs and both the [`Timeout` example](https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#timeout) and [`when` Variants](https://github.com/mxcl/PromiseKit/blob/master/Documentation/GettingStarted.md#when-variants) documentation seem to show that you can use and array of promises, assuming they return the same generic return — MadProgrammer, Jan 05 '19 at 01:27
@MadProgrammer so I can declare the `done` argument as an array and loop through it? — rhlsthrm, Jan 05 '19 at 02:59
In theory (not used PromiseKit for a while), yes, the results “should” be passed to done and should be in the same order — MadProgrammer, Jan 05 '19 at 03:17
I tried to play around it and I couldn't find a way to achieve it... Means that I had to type `result1, result2 ... result100 in` — Ahmad F, Jan 13 '19 at 11:02

score 0 · Accepted Answer · answered Jan 14 '19 at 04:40

0

I was able to solve this the following way (thanks @MadProgrammer):

for index in 0...100 {
    let urlString = "https://someurl.com/item/\(index)"
    guard let url = URL(string: urlString) else { return }
    requestPromises += [URLSession.shared.dataTask(.promise, with: url).validate()]
}

firstly {
    when(fulfilled: requestPromises)
}.done { results in
    // process results
}

answered Jan 14 '19 at 04:40

rhlsthrm

769
1
12
23

1

Ok, so what you should do is to pass only one parameter `results` which refers to the result of each promise, correct? – Ahmad F Jan 14 '19 at 08:34
I am getting: `Contextual type for closure argument list expects 1 argument, which cannot be implicitly ignored` – Ahmad F Jan 14 '19 at 15:32

Swift access closure members programmatically

1 Answers1