message: perf(header): move a branch out of a loop in fmt_comma_delimited
diff: @@ -44,10 +44,12 @@ pub fn from_comma_delimited<T: str::FromStr>(raw: &Raw) -> ::Result<Vec<T>> {
  /// Format an array into a comma-delimited string.
  pub fn fmt_comma_delimited<T: Display>(f: &mut fmt::Formatter, parts: &[T]) -> fmt::Result {
  - for (i, part) in parts.iter().enumerate() {
  - if i != 0 {
  - try!(f.write_str(", "));
  + let mut iter = parts.iter();
  + if let Some(part) = iter.next() {
  + try!(Display::fmt(part, f));
  }
  + for part in iter {
  + try!(f.write_str(", "));
  try!(Display::fmt(part, f));
  }
  Ok(())
  