How to build an Rc or Rc?

As of Rust 1.21.0 and as mandated by RFC 1845, creating an Rc<str> or Arc<str> is now possible:

use std::rc::Rc;
use std::sync::Arc;

fn main() {
    let a: &str = "hello world";
    let b: Rc<str> = Rc::from(a);
    println!("{}", b);

    // or equivalently:
    let b: Rc<str> = a.into();
    println!("{}", b);

    // we can also do this for Arc,
    let a: &str = "hello world";
    let b: Arc<str> = Arc::from(a);
    println!("{}", b);
}

(Playground)

See <Rc as From<&str>> and <Arc as From<&str>>.