Seems to me that the main critique was from someone who didn't understand the specified problem, and complained that this didn't solve a more general one. (...

Seems to me that the main critique was from someone who didn't understand the specified problem, and complained that this didn't solve a more general one. (... and probably wasn't aware that the assumptions made in the specification can be encoded in the API signature in Rust. This wouldn't be possible in C, which is why C forces you to solve the harder problem or rely on your users to not accidentally misuse the data structure.)