chainerror/booksrc/tutorial9.md

Selective Error Handling

What about functions returning different Error types?

In this example func1() can return either Func1ErrorFunc2 or Func1ErrorIO.

We might want to match on func1() with something like:

fn main() -> Result<(), Box<Error>> {
    match func1() {
        Err(e) if let Some(s) = e.downcast_chain_ref::<Func1ErrorIO>() =>
        eprintln!("Func1ErrorIO:\n{:?}", s),

        Err(e) if let Some(s) = e.downcast_chain_ref::<Func1ErrorFunc2>() =>
        eprintln!("Func1ErrorFunc2:\n{:?}", s),
        
        Ok(_) => {}, 
    }
    Ok(())
}

but this is not valid rust code, so we end up doing it the hard way. In the next chapter, we will see, how to solve this more elegantly.

{{#include ../examples/tutorial9.rs}}
# #[allow(dead_code)]
# mod chainerror {
{{#includecomment ../src/lib.rs}}
# }