func ctoz<T>(_ data: T) -> (real: [Float], imag: [Float])
where T: AccelerateBuffer, T.Element == DSPComplex {
  var real = [Float](repeating: 0, count: data.count)
  var imag = [Float](repeating: 0, count: data.count)
  implementation(data, real: &real, imag: &imag)
  return (real, imag)
}

let real = [Float](unsafeUninitializedCapacity: data.count) { r, _ in
  let imag = [Float](unsafeUninitializedCapacity: data.count) { i, _ in
    implementation(data, real: &r, imag: &i)
  }
}
return (real, imag) // use of unresolved identifier imag

let imag: [Float]
let real = [Float](unsafeUninitializedCapacity: data.count) { r, _ in
  imag = [Float](unsafeUninitializedCapacity: data.count) { i, _ in // cannot assign to value: imag is a let constant
    implementation(data, real: &r, imag: &i)
  }
}
return (real, imag)

var imag: [Float]
let real = [Float](unsafeUninitializedCapacity: data.count) { r, _ in
  imag = [Float](unsafeUninitializedCapacity: data.count) { i, _ in // Variable image captured by a closure before being initialized
    implementation(data, real: &r, imag: &i)
  }
}
return (real, imag)