Comment by LoganDark
12 hours ago
> In Rust you can use ?, which is quicker than unwrap, but you also have to do something like Result<Type, Box<dyn std::error::Error>
No, you don't! When returning Result<T, E>, you can use ? on any Result<T2, E2> where E: From<E2>. In other words E doesn't have to be Box<dyn>, it just has to satisfy From<E2>.
Crates like thiserror make it easy to define your own error types that can be easily converted from all the other error types you can encounter in your functions! I do this whenever it doesn't make sense to use an inner error type directly, or whenever a function does its own validation that deserves its own error variant.
On top of that, I tend to also have error variants for each place in the function rather than only for each type of inner error. At error sites I do something like `.map_err(MyError::PlaceInTheFunction)?` rather than only `?`, and then errors become like a very efficient backtrace :)
I think you're proving the author's point.
They're saying that you don't always have to return Result<T, Box<dyn Error>>, you can implement the From<Error> trait on the type and use ? as usual.
In other words implementing that trait lets you set a return type like Result<T, CustomAppError> use ? on it.
I think they're saying the author's point is that it's more fiddly in Rust (even if there are strong, well-regarded fiddles to use)
5 replies →
how so?