I have some question of map function on Collection

  public func map<T>(
    _ transform: (Element) throws -> T
  ) rethrows -> [T] {
    // TODO: swift-3-indexing-model - review the following
    let n = self.count
    if n == 0 {
      return []

i see let n = self.count; if n == 0.
this shouldn’t be ‘if self.isEmpty { … }; let n = self.count’?

You’re talking about here in Collection.swift.

Look a few lines down and you’ll see that n is used as the capacity to reserve in a ContiguousArray. So it is correct as written: the count needs to be found and used.

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The way @Kwanghoon_Choi wrote their suggested edit, it appears that they already believe that n is needed:

If so, I think their issue is with the use of count, which is O(n), over isEmpty, which is O(1). In this case O(n)≈O(1) since n is zero.


ah thanks to reply. it had simple reason.