Rust Builder Pattern

builder.rs

#[derive(Debug)]
struct Builder<'a> {
    args: Vec<&'a str>
}

impl<'a> Builder<'a> {
    fn new() -> Builder<'a> {
        Builder {
            args: Vec::new()
        }
    }
    
    // Builders must consume a mutable self (not a reference) in order to live 
    // long enough to accept changes from oneliners.
    // eg: 
    //      Builder::new().cfg("..").cfg("..");
    fn cfg(mut self, value: &'a str) -> Builder<'a> {
        self.args.push(&value);
        self
    }
    
    // This would fail:
    // let a = Builder::new().cfg_ref("test").cfg_ref("it");
    // |       --------------                              ^ temporary value dropped here while still borrowed
    // |             |
    // |             temporary value created here
    // ...
    // | }
    // | - temporary value needs to live until here
    //
     fn cfg_ref(&mut self, value: &'a str) -> &mut Builder<'a> {
         self.args.push(&value);
         self
     }
}

fn main() {
    let a = Builder::new().cfg("test").cfg("it");
    let a = a.cfg("again").cfg("and").cfg("again");
    println!("{:#?}", &a);
    
    let mut b = Builder::new();
    b.cfg_ref("test");
    println!("{:#?}", &b);
}