macro_rules! dispatch {
    ($(#[$meta:meta])* $vis:vis fn $name:ident$(<$($t:ident: $cons:ident + ?Sized),*>)?(&self $(, $arg:ident: $ty:ty)*) $(-> $out:ty)?) => { ... };
    ($(#[$meta:meta])* $vis:vis fn $name:ident$(<$($t:ident: $cons:ident + ?Sized),*>)?(&mut self $(, $arg:ident: $ty:ty)*) $(-> $out:ty)?) => { ... };
}