Macro failure_ext::err_downcast_ref

macro_rules! err_downcast_ref {
    ( $err:expr ) => { ... };
    ( $err:expr, $($v:ident : $ty:ty => $action:expr),* , ) => { ... };
    ( $err:expr, $v:ident : $ty:ty => $action:expr $(, $rv:ident : $rty:ty => $raction:expr)* ) => { ... };
}

Downcast matching.

Usage:

let res = err_downcast_ref! {
   err,
   ty: Type => { /* use ty as &Type */ },
   yours: YourType => { /* use yours as &YourType */ },
};

Where err is a &anyhow::Error. When one of the type arms match, then it returns Some(value from expr), otherwise None. It's like downcast_ref but for multiple types.