Function downcast_value 

pub fn downcast_value<T>(
    value: Box<dyn Value>,
) -> Result<Box<T>, Box<dyn Value>>
where
    T: Any,

Attempt to downcast a Box<dyn Value> to a concrete type.

Returns Ok(Box<T>) on success and gives the original box back as Err(Box<dyn Value>) on type mismatch.