Add function to get position of named capture

It would be really, really convenient to get the position of a match returned by re.captures("something").name("capture_group_name").

I made a first attempt at implementing it based on what's available, but it's both buggy and inefficient...

extern crate regex;
use regex::{Regex, RegexSet, Captures};


fn get_named_capture_index(caps: &Captures, cap_name: &str) -> Option<usize> {
  let name_string = caps.name(cap_name);
  let mut res: Option<usize> = None;
  if let Some(name_string) = name_string {
    for (cap_ind, _) in caps.iter_pos().enumerate() {
      res = match caps.at(cap_ind) {
        Some(ind_string) => {
          if ind_string == name_string {
            Some(cap_ind)
          } else {
            None
          }
        },
        None => None
      };
    }
  }
  res
}

fn get_named_capture_position(caps: &Captures, cap_name: &str) ->
  Option<(usize, usize)> {
    let cap_ind = get_named_capture_index(caps, cap_name);
    if let Some(cap_ind) = cap_ind {
      caps.pos(cap_ind)
    } else {
      None
    }
}

[BurntSushi]

This should be fixed once 1.0 is released. Specifically, the name (and at/get) methods now return a Match, which includes both the position information and the matched substring. See here: https://github.com/rust-lang-nursery/regex/blob/rfc/src/re_unicode.rs#L926

A work around you could use today is to build a map of capture name to index for the entire regex using capture_names, which returns an iterator of Option<&str>. You'd only have to do this once for each regex, and you could look up the name in that map to get the capture index, and then you could use your get_named_capture_position function.

Thanks for the workaround! If anyone else happens on this ticket before 1.0, here is what I wrote following your advice:

fn get_named_capture_index(re: &Regex, cap_name: &str) -> Option<usize> {
  re.capture_names().position(|name| {
    name == Some(cap_name)
  })
}

fn get_named_capture_position(re: &Regex, caps: &Captures, cap_name: &str) ->
  Option<(usize, usize)> {
    let cap_ind = get_named_capture_index(re, cap_name);
    if let Some(cap_ind) = cap_ind {
      caps.pos(cap_ind)
    } else {
      None
    }
}