Given a blanket impl `impl<T: Display> ToString for T`, you also want to write `impl ToString for MyType` to customize it. What happens when you compile both, and why?
impl<T: Display> ToString for T {
fn to_string(&self) -> String { /* ... */ }
}
struct MyType;
impl ToString for MyType {
fn to_string(&self) -> String { String::from("custom") }
}