Allow only 1 attachment to a promise

[beckje01]

Doing something like the following should not be allowed:

get { HttpClient httpClient ->
    def respPromise = httpClient.get {
        it.url.set(new URI("http://badsite.gas"))
    }

    respPromise.onError {
         //...
    }

    respPromise.then {
         //...
    }
}

We should error if you try to attach to the same promise twice.

[uris77]

What is the correct way to add an error handler? The intuitive thing to do, in my opinion, is something like what we have in javascript:

returnaPromise().then(funcA, errorFunc)

or:

returnAPromise().then(funcA).fail(erroFunc).done(funcB)

I feel like I'm missing something.

[ldaley]

Use promise.onError().then().

[uris77]

Ah, thanks. I was doing it the wrong way: promise.then().onError()