I'd like to write a library that's a thin wrapper around some of the functionality in BTreeMap. I'd prefer not to tightly couple it to that particular data structure though. Strictly speaking, I only need a subset of its functionality, something along the lines of the NavigableMap interface in Java. I was hoping to find an analogous trait I could use. I seem to recall that at some point there were traits like Map and MutableMap in the standard library, but they seem to be absent now.
Is there a crate that defines these? Or will they eventually be re-added to std?
No, right now there's only Iterator. MutableMap and Map have been removed somewhere along the road to stabilization of std for Rust 1.0.
There have been various discussions about re-adding traits to std. See these discussions on Rust internals:
or (less recent but more specifically on collections):
Bottom line: everybody wants some form of those traits in std but nobody wants to commit adding and supporting the wrong ones in the standard library until a clearer picture of what is ergonomic emerges.
来源：https://stackoverflow.com/questions/35159530/does-rust-have-collection-traits