type
  sharedStringObj = object
    len: int
    sptr: pointer

  sharedString* = ptr sharedStringObj

proc newSharedString*(s: cstring = nil): sharedString =
  result = cast[sharedString](allocShared0(sizeof(sharedStringObj)))
  if s.len != 0:
    result.len = s.len
    result.sptr = allocShared0(s.len)

    var
      ssc = cast[cstring](result.sptr)
    for i in 0 .. s.len-1:
      ssc[i] = s[i]

proc freeSharedString*(ss: var sharedString) =
  if not ss.isNil:
    if not ss.sptr.isNil and ss.len != 0:
      ss.sptr.deallocShared()
      ss.len = 0
      ss.sptr = nil
    ss.deallocShared()
    ss = nil

proc `$`*(ss: sharedString): string =
  result = $(cast[cstring](ss.sptr))

proc `&`*(ss: sharedString, c: char|string|cstring|sharedString): string =
  $ss & $c

proc test() =
  var
    a = newSharedString()
    b = newSharedString("abc")
    c = newSharedString("def".cstring)

  defer:
    a.freeSharedString()
    b.freeSharedString()
    c.freeSharedString()

  echo a
  echo b
  echo c

  echo b & 'c'
  echo b & "d"
  echo b & "e".cstring
  echo b & c

when isMainModule:
  test()