src/main.rs：

struct FooError;

struct OneError;

struct TwoError;


impl From<OneError> for FooError {
    fn from(_: OneError) -> Self {
        FooError
    }
}

impl From<TwoError> for FooError {
    fn from(_: TwoError) -> Self {
        FooError
    }
}

fn my_test_fn() -> Result<(), FooError> {
    let one: Result<(), OneError> = Err(OneError);
    one?;

    let two: Result<(), TwoError> = Err(TwoError);
    two?;

    Ok(())
}

fn main() {
    let result = my_test_fn();
    println!("error? {}", result.is_err());
}