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use std::str::FromStr;
 
impl<A:FromStr,B:FromStr> FromStr for (A,B) {
    type Err = String;
    fn from_str(s: &str) -> Result<Self,Self::Err> {
        let mut xs = s.split_whitespace();
        Ok((xs.next().unwrap().parse().ok().unwrap(),
            xs.next().unwrap().parse().ok().unwrap()))
    }
}
 
fn main() {
    let s = "3 4";
 
    let (a, b): (i32, i32) = s.parse().unwrap();
 
    println!("{:?} {:?}", a, b);
 
}
 
 

error[E0210]: type parameter `A` must be used as the type parameter for some local type (e.g. `MyStruct<T>`); only traits defined in the current crate can be implemented for a type parameter
  --> prog.rs:3:1
   |
3  | impl<A:FromStr,B:FromStr> FromStr for (A,B) {
   | ^

error: aborting due to previous error

Standard output is empty