playground.rs

use std::error::Error;
use std::str::FromStr;

fn main() {
    let s = "r5";
    let x = i32::from_str(s).map_err(foo);
    x.map_err(|v| println!("{}", v.description()));
}

fn foo<'a, A>(a: A) -> Box<Error + 'a>

playground.rs

use std::error::Error;


fn main() {
    println!("Hello, world!");
}

fn foo<'a, A>(a: A) -> Box<Error + 'a>
    where A: Error + 'a
{

playground.rs

use std::error::Error;


fn main() {
    println!("Hello, world!");
}

fn foo<A>(a: A) -> Box<Error> where A: Error {
    Box::new(a)
}