Read lines in Swift

readlines.swift

// known good: Swift 4.2

import Foundation

/// Returns an iterator that iterates through the lines of the file at path.
///
/// - Parameter path: path of the file to read
/// - Returns: the iterator, or nil if the file could not be read
func lineSequence(forFileAtPath path:String) -> AnyIterator<String>?
{
  guard let handle = FileHandle.init(forReadingAtPath: path) else { return nil }
  let filePtr = fdopen(handle.fileDescriptor,
                       "r".cString(using: String.Encoding.ascii)!)

  return AnyIterator({ () -> String? in
    var line:UnsafeMutablePointer<Int8>? = nil
    var linecap:Int = 0
    defer { free(line) }

    if getline(&line, &linecap, filePtr) > 0,
      let cStringLine = UnsafePointer<CChar>(line)
    {
      return String(cString: cStringLine)
    }
    else {
      return nil
    }
  })
}