Why AnyHistory is an enum and not a wrapper around Box<dyn History>

[Neo-Ciber94]

I'm browsing through the repository to know how can I implement by own router, and I found this:

/// A [`History`] that provides a universial API to the underlying history type.
#[derive(Clone, PartialEq, Debug)]
pub enum AnyHistory {
    /// A Browser History.
    Browser(BrowserHistory),
    /// A Hash History
    Hash(HashHistory),
    /// A Memory History
    Memory(MemoryHistory),
}

I think this make hard to add your own implementation, why AnyHistory is not implemented as:

pub struct AnyHistory {
   imp: Box<dyn History>
}

[futursolo]

Boxing a struct involves an additional allocation and using enumerate can avoid the allocation.

The History trait is also not object safe (required for boxing) as it uses generics on its methods.