Hello,
I had a question about the intended behavior/functionality of mirrors in Swift/Swift Foundation types.
In general, should a Mirror reference all variables in a type?
I’m not sure what scope mirrors should/will have, but it does seem like some of iterating through children has been done:
How can I check if a property has been set using Swift reflection? - Stack Overflow
Should mirrors only reference public+ variables? Or private ones too? Is it meant to be up to the author?
There exists a default behavior, but also an override mechanism (CustomReflectable) in case the author of the type knows better
For instance, if you have
struct Point { var x: Double; var y: Double }
you probably do just want to see "x" and "y" reflected - and the default will do just that
But in more complex scenarios, e.g. Array<T>, you probably want to see the logical contents of the type (the array elements), not the underlying implementation details
I don't think metadata currently vends visibility, so it's unlikely we do anything to hide non-public variables in reflection.
I think other languages take a similar stance, so maybe it's just the right thing to do, but I also can't recall any explicit discussion about this
As for the Foundation-specific bits, I'll let somebody with more Foundation expertise help you out
With respect to Foundation, I was starting to silence some warnings with ‘as Any’ (https://bugs.swift.org/browse/SR-2737\), but I noticed this code in URLComponents.swift at https://github.com/apple/swift-corelibs-foundation/blob/master/Foundation/URLComponents.swift#L313:
if let s = self.scheme { c.append((label: "scheme", value: s)) }
if let u = self.user { c.append((label: "user", value: u)) }
etc...
Should public properties be mirrored even if their values are nil?
c.append((label: "scheme", value: s as Any))
c.append((label: "user", value: u as Any))
etc...
What rules should there be to determine what gets mirrored?
Regards,
Will Stanton
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Thanks,
- Enrico
egranata@.com 27683
···
On Sep 22, 2016, at 10:08 PM, Will Stanton via swift-dev <swift-dev@swift.org> wrote: