Macro downcast_rs::impl_downcast

macro_rules! impl_downcast {
    (@ impl_full $trait_ : ident [$($param_types : tt) *] for
 [$($forall_types : ident), *] where [$($preds : tt) *]) => { ... };
    (@ impl_full_sync $trait_ : ident [$($param_types : tt) *] for
 [$($forall_types : ident), *] where [$($preds : tt) *]) => { ... };
    (@ impl_body $trait_ : ident [$($types : tt) *]) => { ... };
    (@ impl_body_sync $trait_ : ident [$($types : tt) *]) => { ... };
    (@ inject_where [$($before : tt) *] types [] where [] [$($after : tt) *]) => { ... };
    (@ inject_where [$($before : tt) *] types [$($types : ident), *] where []
 [$($after : tt) *]) => { ... };
    (@ inject_where [$($before : tt) *] types [$($types : ident), *] where
 [$($preds : tt) +] [$($after : tt) *]) => { ... };
    (@ as_item $i : item) => { ... };
    ($trait_ : ident) => { ... };
    ($trait_ : ident < >) => { ... };
    (sync $trait_ : ident) => { ... };
    (sync $trait_ : ident < >) => { ... };
    ($trait_ : ident < $($types : ident), * >) => { ... };
    (sync $trait_ : ident < $($types : ident), * >) => { ... };
    ($trait_ : ident < $($types : ident), * > where $($preds : tt) +) => { ... };
    (sync $trait_ : ident < $($types : ident), * > where $($preds : tt) +) => { ... };
    ($trait_ : ident assoc $($atypes : ident), *) => { ... };
    (sync $trait_ : ident assoc $($atypes : ident), *) => { ... };
    ($trait_ : ident assoc $($atypes : ident), * where $($preds : tt) +) => { ... };
    (sync $trait_ : ident assoc $($atypes : ident), * where $($preds : tt) +) => { ... };
    ($trait_ : ident < $($types : ident), * > assoc $($atypes : ident), *) => { ... };
    (sync $trait_ : ident < $($types : ident), * > assoc $($atypes : ident), *) => { ... };
    ($trait_ : ident < $($types : ident), * > assoc $($atypes : ident), * where
 $($preds : tt) +) => { ... };
    (sync $trait_ : ident < $($types : ident), * > assoc $($atypes : ident), *
 where $($preds : tt) +) => { ... };
    (concrete $trait_ : ident < $($types : ident), * >) => { ... };
    (sync concrete $trait_ : ident < $($types : ident), * >) => { ... };
    (concrete $trait_ : ident assoc $($atypes : ident = $aty : ty), *) => { ... };
    (sync concrete $trait_ : ident assoc $($atypes : ident = $aty : ty), *) => { ... };
    (concrete $trait_ : ident < $($types : ident), * > assoc
 $($atypes : ident = $aty : ty), *) => { ... };
    (sync concrete $trait_ : ident < $($types : ident), * > assoc
 $($atypes : ident = $aty : ty), *) => { ... };
}

Adds downcasting support to traits that extend downcast::Downcast by defining forwarding methods to the corresponding implementations on std::any::Any in the standard library.

See https://users.rust-lang.org/t/how-to-create-a-macro-to-impl-a-provided-type-parametrized-trait/5289 for why this is implemented this way to support templatized traits.