Closure passed to flatMap needs return type specified?

[wvteijlingen]

Maybe I'm missing something here, but it seems like I must specify the return type of the closure passed to flatMap. When I use just the parameters, it fails to build with error: "Missing argument for parameter 'f' in call".

Doesn't work:

Artist.findOne("1").flatMap { resource, meta in
    return resource.findRelated("albums")
}

Does work:

Artist.findOne("1").flatMap { resource, meta -> Future<([Resource], Meta?)> in
    return resource.findRelated("albums")
}

[Thomvis]

I think Swift only is able to deduce the type of a closure if it is a single expression, without return.

This does not work:

future(1).flatMap { num in
    return Future.succeeded(num);
}

This does work:

future(1).flatMap { num in
   Future.succeeded(num);
}

So, I'm guessing that this will also work:

Artist.findOne("1").flatMap { resource, meta in
   resource.findRelated("albums")
}

[wvteijlingen]

You're right! Weird though, because the second closure has a return as well, it's just implicit.