Besides the learning difficulty, I'd there are some real ergonomic issues related to ownership, such as the difficulty of cloning into a closure [1], or nested

Besides the learning difficulty, I'd there are some real ergonomic issues related to ownership, such as the difficulty of cloning into a closure [1], or nested &mut receiver calls being rejected despite being sound [2]. [1] https://github.com/rust-lang/rfcs/issues/2407 https://github.com/rust-lang/rfcs/issues/2407 [2] https://github.com/rust-lang/rust/issues/6268 https://github.com/rust-lang/rust/issues/6268