The opposite function of unwrap (Unwrap error)

help
1

Hello.
I am looking for a function that will be the opposite of the unwrap () function.
I would like to conveniently write unit tests.

  1. Is such a feature in the standard library?

  2. I made a function like this:

pub fn unwrap_err<T, E>(result: std::result::Result<T, E>) -> E {
    match result
    {
        Ok(_) => { panic!("should be error!"); },
        Err(e) => { return e; }
    };
}

Unwrap Error

  1. How do you convert it (unwrap_err) into a feature and add it to the structure?
// ???
pub trait UnwrapError<T, E> 
{
    fn unwrap_error(self, _: T, e: E) -> E 
    where Self: Sized 
    {
        let x = unwrap_err(self);
        return x;
    }
}
 
fn main()
{
    let x = ... ; // my struct
    let err = x.unwrap_error(); // panic if OK 
}
2

  • Result::unwrap_err() in the standard library

  • trait UnwrapError {
    type Error;
    
    fn unwrap_error (self: Self)
      -> Self::Error
    ;
}

impl<Ok, Err> UnwrapError for Result<Ok, Err> {
    type Error = Err;
    
    fn unwrap_error (self: Result<Ok, Err>)
      -> Err
    {
        match self {
            | Ok(_) => panic!("`.unwrap_error()`: unexpect `Ok` variant"),
            | Err(it) => it,
        }
    }
}
1 Like
3

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