Swift programming question from my son

[Steve Caine]

C++ was notorious for obscure compiler errors; 10-15 lines of error message that had to be boiled down as text (using find/replace in a text editor) to reveal you were trying to assign to a const object. Perhaps the compilers are better these days.

— 
Steve Caine
http://www.linkedin.com/in/stevecaine

> On Oct 10, 2015, at 12:09 PM, John Shockey <john at johncshockey.com> wrote:
> 
> Owen,
> 
> I haven't done a lot with Swift, since my current project predates the
> language. I can't make a lot of sense of the error message. It's a
> pretty bad one!
> 
> But I can see where the difference between the two versions would
> matter.
> 
> if label.userData != nil
> {
>    // ...
> }
> 
> tells you that userData won't be nil within the braces. But
> 
> if var userData = label.userData
> {
>    // ...
> }
> 
> tells both you AND the compiler that it isn't nil
> 
> So in their version userData is typed as a dictionary, but in your son's
> version label.userData is still typed as an optional dictionary.
> 
> Seems pretty academic, but in fact another thread could set
> label.userData to nil, but the "if var" would be protected. But the real
> point is about the types.
> 
> Possibly (but I have not done a lot with Swift, remember, so I'm a
> little unsure of the syntax) adding a couple of "!" operators would make
> his version work. Maybe:
> 
>    label.userData!["bounceCount"] = (label.userData!["bounceCount"] as!
>    Int) + 1
> 
> but don't quote me on that without checking it!
> 
> My feeling is that comparing something to nil in Swift may be legal, and
> sometimes work, but it kind of goes against the grain of the language.
> 
> John
> 
> _______________________________________________
> MacTechGroup-discuss mailing list
> MacTechGroup-discuss at lists.mactechgroup.org
> http://lists.mactechgroup.org/mailman/listinfo/mactechgroup-discuss