http/
convert.rs

1macro_rules! if_downcast_into {
2    ($in_ty:ty, $out_ty:ty, $val:ident, $body:expr) => {{
3        if std::any::TypeId::of::<$in_ty>() == std::any::TypeId::of::<$out_ty>() {
4            // Store the value in an `Option` so we can `take`
5            // it after casting to `&mut dyn Any`.
6            let mut slot = Some($val);
7            // Re-write the `$val` ident with the downcasted value.
8            let $val = (&mut slot as &mut dyn std::any::Any)
9                .downcast_mut::<Option<$out_ty>>()
10                .unwrap()
11                .take()
12                .unwrap();
13            // Run the $body in scope of the replaced val.
14            $body
15        }
16    }};
17}