Why should I prefer `Option::ok_or_else` instead of `Option::ok_or`?

Question

I just saw the following change in a pull request:

- .ok_or(Error::new(ErrorKind::Other, \"Decode error\"));
+ .ok_o         


        

Answer 1

The signature of std::io::Error::new is

fn new(kind: ErrorKind, error: E) -> Error 
where
    E: Into>, 

This means that Error::new(ErrorKind::Other, "Decode error") allocates memory on the heap because error needs to be converted into Box to be of any use.

Consequently, this pull request removes unneeded memory allocation/deallocation when the Result value is Result::Ok.