> On Dec 29, 2015, at 4:50 PM, Austin Zheng via swift-dev <swift-dev@swift.org>
> wrote:
>
> Hello,
>
> First, some background. I'm currently working on refactoring the way mirrors
> are handled within the Swift standard library (conversion from use of
> _Reflectable and _MirrorType to CustomReflectable).
>
> Note that the _MirrorType protocol exposes an 'objectIdentifier' property
> which is only relevant for class instances. Each type's mirror would have to
> manually implement this property, with mirrors for non-class types expected
> to return nil.
>
> CustomReflectable moves away from each type having a custom
> _MirrorType-conforming mirror type in favor of using Mirror for everything,
> which means that certain manually specified properties such as
> 'objectIdentifier' and 'summary' disappear, and must be replaced by other
> language features.
>
> Now, the current way I distinguish between classes and non-class types (for
> the dump() function) is through the following code (variable names are made
> up):
>
> if let thisClassThing = thisThing as? AnyObject {
> let theIdentifier = ObjectIdentifier(thisClassThing)
> // do other stuff...
> }
>
> (In the context of dump(), this is necessary to ensure that dumping an object
> with a cycle of references doesn't result in infinite recursion.)
>
> However, where this breaks down is when Foundation is imported. In this case,
> performing as? or is casts/checks on a bridged Swift type such as String or
> Array<T> results in the test returning true or the type being bridged to an
> NS* object type.
>
> My question is whether or not there exist tools in the stdlib to determine
> whether an instance is an instance of a class or not, while also being able
> to distinguish between native Swift bridgeable structs and their NS*
> equivalents. I have a few ideas I'm exploring but I wanted to run this
> question by the community first to see if there's anything I'm missing, or if
> anyone has any good ideas.
>
> Thanks for your time, and if you have any questions I'd be happy to clarify.
You can ask if `thisThing.dynamicType is AnyObject.Type`, since the metatypes
of bridgeable types don't themselves bridge.
-Joe
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