Read a file one line at a time in Swift

SwiftLineReader.swift

import Darwin

/**
 Returns a lazy sequence that returns a String for every line of `file`.
 
 Example 1:
 // print all lines from a file
 let file = fopen(NSBundle.mainBundle().pathForResource("Cartfile", ofType: nil)!,"r")
 for line in lineGenerator(file) { print(line,separator: "", terminator: "") }
 fclose(file)
 
 Example 2:
 // echo lines from stdin
 for line in lineGenerator(stdin) { print(line, separator: "", terminator: "") }

 */
func lineGenerator(file:UnsafeMutablePointer<FILE>) -> AnyGenerator<String>
{
  return AnyGenerator { () -> String? in
    var line:UnsafeMutablePointer<CChar> = nil
    var linecap:Int = 0
    defer { free(line) }
    return getline(&line, &linecap, file) > 0 ? String.fromCString(line) : nil 
  }
}

let p = "/path/to/file"  // could be returned by NSBundle.pathForResource, if we were using Foundation
let f = fopen(p,"r")
let g = lineGenerator(f)
for line in g {
  // suppress print's automatic line ending, since
  // lineGenerator captures every line's own new line character.
  print(line, separator: "", terminator: "")
}

Note: From Rev 5 to Rev 6 (posted 2016-04-30T21:36PST), I changed line 22, which frees the temporary line buffer created by getline.

I believe the earlier line line.destroy() was incorrect, or at least probably incorrect, since it's not clear to me what the Swift docs mean by "object" in that context. Does line.destroy() destroy the C array starting at that char or just the first char?

But since the buffer is created by getline, it's created by malloc or its friends so free should be the correct balancing call.

Your snippet made me learn more about Sequence and how to define a custom one.
Thanks!

Wrapped your code inside swift class in this gist