Builder pattern in rust

use std::collections::HashMap;
struct UrlBuilder {
    queries: HashMap<String, String>,
    base_url: String

}

impl UrlBuilder {
    pub fn new(base_url: &str) -> Self{
        Self {base_url: String::from(base_url), queries: HashMap::new()}
    }

    pub fn as_string(&self) -> String {
        let mut query_string = String::new();
        for (k, v) in &self.queries {
            query_string = match query_string.as_str() {
                "" => format!("?{}={}", k, v),
                _ => format!("{}&{}={}", &query_string, k, v)
            };
        }
        format!("{}/{}", self.base_url, query_string)
    }
    
    // This is the part where the magic happens
    // We changing the inner values (queries) and returning a 
    // mutable self object with lifetime 'a.     
    pub fn limit<'a>(&'a mut self, value: i32) -> &'a mut Self {
        self.queries.insert(String::from("limit"), format!("{}", value));
        self
    }
    pub fn search<'a>(&'a mut self, word: &str) -> &'a mut Self  {
        self.queries.insert(String::from("search"), String::from(word));
        self
    }
}

fn main() {
   println!("{}", 
        UrlBuilder::new("https://example.com")
           .limit(10)
           .search("word")
           .as_string()
   )