Replace with captured groups? about rust-onig HOT 5 CLOSED

You are right, onig implements replacement. The second argument to the replace family of fuctions is a Replacer. This can either be a literal string, a callback which takes the capture group and returns a astring, or some custom instance of your own type.

If you want to use the captures in the replacement the quickest way would probably be to format the captures yourself:

let result = re.replace_all("first second", |caps: &Captures| {
    format("{} {}", caps.at(2).unwrap(), caps.at(1).unwrap())
});

Check out the docs for more information.

from rust-onig.

But onig doesn't support $1 and etc when providing only replacement string, right?

from rust-onig.

No. The replacements that onig supports out of the box are:

• Literal strings, with no support for capture group references
• Callbacks to produce a replacement from the captured content

You could add support for dollar-string syntax quite easily though:

use onig::{Regex, Replacer, Captures};
use std::borrow::Cow;

/// A string, with `$1` refering to the first capture group.
struct Dollarified<'a>(&'a str);

impl <'a> Replacer for Dollarified<'a> {
    fn reg_replace(&mut self, caps: &Captures) -> Cow<str> {
        let mut replacement = self.0.to_owned();
        for i in 1..caps.len() {
            replacement = replacement.replace(
                &format!("${}", i),
                caps.at(i).unwrap());
        }
        replacement.into()
    }
}

fn main() {
    let re = Regex::new(r"(\w+) (\w+)").unwrap();
    let hay = "hello world";
    println!("{} -> {}", &hay, re.replace(hay, Dollarified("$2 $1")));
}

I can't vouch for the efficiency of the above code. If you know the format of the replacement then using a closure instead is going to be quicker.

from rust-onig.

Ok, I see.
Then I suppose user should go with callback to handle it.
Thanks.

from rust-onig.

I've added an example which shows a better implementation of dollar replacement strings. It is probably something we should support in this crate. More work is needed though to decide on the exact replacement syntax (do we support named captures, what does an invalid number expand to and so on).

Thanks for the question though!

from rust-onig.