It's how you explicitly cast from one type to another. To use the ? operator with a custom error type, it needs to be converted to the std error type.
Re:Things I Enjoy in Rust: Error Handling
by steveklabnik on Monday April 22, 2019 @04:44PM
(#19722795)
It needs to be converted to whatever error type the function returns. That can be anything.
It it safe to just put a noop in there? What's From-ness? Is QuestionError defined in std? Where do I read more?
EDIT: oh I see, I didn't read carefully. I just need to provide a conversion. Your example is very clear.