trait_solving.rs

trait Hello {
  fn say_hello() -> Self;
}
impl Hello for i32 {
  fn say_hello() -> i32 {
    println!("hello i32");
    0i32
  }
}
impl Hello for usize {
  fn say_hello() -> usize {
    println!("hello usize");
    0usize
  }
}
fn main() {
  // by annotating the return type is `i32`,
  // compiler can resolve to the trait implementation of `i32`
  let res: i32 = Hello::say_hello();
  
  // by annotating the return type is `usize`, 
  // compiler can resolve to the trait implementation of `usize`
  let res: usize = Hello::say_hello();
}