Code shared from the Rust Playground

playground.rs

extern crate regex;

use regex::RegexBuilder;
use std::fmt::Write;

fn main() {
    let query = "is";
    let mut query_as_string = String::from("");
    
    if true {
        write!(query_as_string, r"\b{}\b", query).unwrap();
    } else {
        write!(query_as_string, r"{}", query).unwrap();
    }
    
    let mut regex_builder = RegexBuilder::new(&query_as_string);
    regex_builder.case_insensitive(true);
    let regex = regex_builder.build().unwrap();
    
    let text = "Retroactively relinquishing remunerations is reprehensible.";
    for mat in regex.find_iter(text) {
        println!("{:#?}", mat.start());
    }
}