Translating tuple to array?

Question

I'm accessing a C language struct in my Swift project that stores data as a tuple and I want to iterate over it.

let tuple = (1, 2, 3, 4, 5)

AFAIK, I have two options. The first is to mirror the tuple so that I can map its reflection into an array:

let tupleMirror = Mirror(reflecting: tuple)
let tupleArray = tupleMirror.children.map({ $0.value }) as! [Int]

And the second option is to translate it into an array using manual memory management with something like an unsafe buffer pointer. From all that I've read, it's usually suggested to avoid the manual-memory route if possible and Mirror certainly appears to do that. Is mirroring a safe/reliable way to convert a tuple to an array? Or is there a better approach to translating the tuple into an array or even iterating over the tuple itself?

Is your tuple always of arbitrary length? Why do you want to keep it as a tuple? Why don't use array from the beginning? — Maxim Kosov
– Maxim Kosov, Commented Mar 17, 2020 at 15:25
@MaximKosov The length is constant. And I don't want to keep it as a tuple. In my example, I've translated it to an array. And modifying the C code is not an option (third-party dependency). — lurning too koad
– lurning too koad, Commented Mar 17, 2020 at 15:27
So, if the length is constant, say 5, can you just write a regular function? Like let arr = [tuple.0, tuple.1, ...]? — Maxim Kosov
– Maxim Kosov, Commented Mar 17, 2020 at 15:29
Looks like on the apple forums they suggest to use UsafeBufferPointer. forums.developer.apple.com/thread/72120 — Maxim Kosov
– Maxim Kosov, Commented Mar 17, 2020 at 15:32
I don't think tuple could be not constant size, to be honest — Maxim Kosov
– Maxim Kosov, Commented Mar 17, 2020 at 15:33

user652038 · Accepted Answer · 2020-03-17 16:12:21Z

5

Mirror is fiiiiiiiiiiiiine.

extension Array {
  init?<Subject>(mirrorChildValuesOf subject: Subject) {
    guard let array = Mirror(reflecting: subject).children.map(\.value) as? Self
    else { return nil }

    self = array
  }
}

  XCTAssertEqual(
    Array( mirrorChildValuesOf: (1, 2, 3, 4, 5) ),
    [1, 2, 3, 4, 5]
  )

  XCTAssertNil(
    [Int]( mirrorChildValuesOf: (1, 2, "3", 4, 5) )
  )

answered Mar 17, 2020 at 16:12

user652038

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