1 | macro_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 | } |
18 | |