I am not sure if this directly applies to your post, but it came to mind when I read the section about `extern crate`. It seems like the Cargo system is relied

I am not sure if this directly applies to your post, but it came to mind when I read the section about `extern crate`. It seems like the Cargo system is relied upon by almost all Rust users, and I am not sure if the following is an ergonomics problem or a lack of understanding on my part. A couple months ago I was exploring Rust's web server capabilities after seeing the "Are we web yet?" page. I decided to try out the `iron` package.[0] I was quickly able to serve some basic content, but I wanted to add some headers to the response. I was able to `use iron::headers::Allow` to add an Allow header.[1] Next, I wanted a Link header. Link wasn't available but I could get around that by defining a custom header with the `header!` macro. Unfortunately, I couldn't figure out how to get the `header!` macro for custom headers without `#[macro_use] extern crate hyper` and adding `hyper` to the Cargo.toml file.[2] Then I wanted a `Vary` header. I was able to get that in with `use iron::headers::Vary`, but I couldn't actually create one yet! In order to create my `Vary::Items` header, I needed to also `use unicase::UniCase` and add `unicase` to my Cargo.toml.[3][4] So within an hour or so of starting the project, my explicitly listed dependencies had grown from just `iron` to include two additional dependencies. The iron package already relies upon hyper which already relies upon unicase. Here are some questions I am still left with. Would love any responses. Is it possible for me to use the pieces described above without explicitly listing these crates? If not, why do I need to declare hyper as a dependency when iron is already using it? Perhaps I don't need to, and I was just unable to figure out how to get the `header!` macro from iron directly. My initial expectation was that iron would either wrap or expose every part of hyper that I might need. The same goes for hyper not allowing me to just use the same unicase it relies upon. How am I supposed to get the correct version of hyper and unicase to match with the ones that my version of iron was sent with? Do I have to go look them up? Can use the latest version of `hyper` even if `iron` is a few versions behind? What version should I be specifying? [0]: http://ironframework.io/doc/iron/ http://ironframework.io/doc/iron/ [1]: http://ironframework.io/doc/iron/headers/struct.Allow.html http://ironframework.io/doc/iron/headers/struct.Allow.html [2]: https://hyper.rs/hyper/v0.9.9/hyper/macro.header!.html https://hyper.rs/hyper/v0.9.9/hyper/macro.header!.html [3]: http://ironframework.io/doc/iron/headers/enum.Vary.html http://ironframework.io/doc/iron/headers/enum.Vary.html [4]: http://ironframework.io/doc/unicase/struct.UniCase.html http://ironframework.io/doc/unicase/struct.UniCase.html