> The optimized and stripped library in rust was about 8 times the size of the C version. While 9MB is not a lot by itself, if a significant portion of libraries decide they want to switch to rust that would explode disk usage!

The underlying issue is that even though the standard library is statically linked, Rust does not make it easy to compile "custom" builds of the standard library as part of your project - which leaves you with all sorts of excess code bloat in the final build. You can solve this, but it requires unofficial tools such as "xargo" and the like. Once this is addressed, Rust should become genuinely competitive with C/C++ (wrt. binary size).

See also https://news.ycombinator.com/item?id=23496107 for the details.