> On 4 Oct 2015, at 18:56, Rick Mann <rm...@latencyzero.com> wrote:
>
>
>> On Oct 3, 2015, at 23:03 , Roland King <r...@rols.org> wrote:
>>
>> Apply the usual swift technique and break it down into more than one line
>> then go look at the types of each variable.
>>
>> let ff = device.formats
>> let pp = ff!
>>
>> option-click on each of those variables and you’ll quickly see the ‘!!’ on
>> the first one and hence why you have to explicitly unwrap it to get it into
>> a [AnyObject] which has a generator.
>
> A) Ah, so it's Swift continuing to suck.
No, not at all, Swift is being consistently consistent. The variable is a ‘!!’
which means it’s implicitly unwrapped optional of an implicitly unwrapped
optional of an array, so when you use it it gets unwrapped for you, once, thus
leaving an implicitly unwrapped optional and optionals don’t have generators,
you have to re-unwrap it again.
> B) Why is device.formats double-bang?
I believe (every time I say that Quincey sharpens his keyboard) it’s because
you’re calling formats() on an AnyObject. Swift knows formats() returns an
Array of AnyObject, well an optional one, but it doesn’t know if the AnyObject
you’re calling it on actually supports the method/property ‘formats’. So the
first optional is ‘was I able to even call formats on this AnyObject’ and the
second optional is the result. So you can disambiguate between the object not
having a formats property and it having a formats property which doesn’t have
any formats.
If you explicitly format devices as [ AVCaptureDevice ], either when you
declare it or when you use it in the for loop
for device in devices as [ AVCaptureDevice ]
then device becomes an AVCaptureDevice and the second optional goes away.
> C) Why can't I option-click on formats in device.formats to get an answer
> (because A)?
More likely because of B. Again if you cast the devices so each device is an
AVCaptureDevice then option-click works.
> D) Why does command-clicking on formats take me to an Obj-C file (because A)?
No clue - I did it in a playground for speed and Command-clicking doesn’t do
much in playgrounds at the best of times. Does it do better if you’ve strongly
typed device?
>
> Thanks for pointing out you can get the type of a variable by option-clicking
> it like that. Not sure why it doesn't consistently work (e.g. why can't I get
> the type of formats), but that'll be very helpful.
If it wasn’t for option-click I think I would have thrown Swift down a deep
hole by now. My two techniques when faced with an error such as the above are
either split into multiple lines and use Option-Click or, knowing it’s usually
a mismatch between what I think a variable is and what Swift thinks a variable
is, explicitly type things until either the error goes away, or Swift tells me
why what I think the variable is, is wrong.
Generally if you find yourself doing something with [AnyObject] (and there’s
less of that with the new typed collections in ObjC) you should smell the whiff
wafting up through the code and do a cast to something stronger-typed, then
Swift can do a better job of helping you help yourself, and assert brutally if
the type isn’t what you thought it was going to be.
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