Rust 返回“空”泛型变量

Question

I want to have a function that let me extract infos from Results. The problem is what to return if something fails (the function uses a generic parameter). Here is my code:

fn check<T, E>(x: Result<T, E>) -> T {
    if let Ok(sk) = x {
        return sk;
    } else {
        println!("uh oh");
        return 0 as T;
    }
}

As you can guess it doesn't work, what should i put instead of 0 as T ?

Answer 1

If you want to return the default value for the type (0 for numbers, false for bools, an empty string for strings etc.) you can constrain it to T: Default and return T::default() :

fn check<T: Default, E>(x: Result<T, E>) -> T {
    if let Ok(sk) = x {
        return sk;
    } else {
        println!("uh oh");
        return T::default();
    }
}

But note that there is an existing method on Result that returns the default value in case of Err : unwrap_or_default() .