Audit headers for nullability (Swift support)

[1ec5]

Once we distribute a framework (#828), developers will be able to interface with MGLMapView and other classes in Swift. We’ll want to audit the headers for nullability so that developers don’t have to deal with a litany of implicitly unwrapped optionals like NSString!.

More information:

• https://developer.apple.com/swift/blog/?id=25
• http://nshipster.com/swift-1.2/#nullability-annotations

[incanus]

👍

[1ec5]

After #975 is merged, this work will still be blocked by travis-ci/travis-ci#3216 because the nullability qualifiers will still go into the Objective-C code that Travis builds.

[1ec5]

Apparently this isn’t completely blocked: Automatic uses conditionally-compiled macros to declare nullability:

#if __has_feature(nullability)
#define mgl_nonnull nonnull
#define mgl_nullable nullable
// …
#else
#define mgl_nonnull
#define mgl_nullable
// …
#endif

[1ec5]

Or, come to think of it, even just:

#if !__has_feature(nullability)
#define nonnull
#define nullable
// …
#endif