Having a GC also kind of makes it nasty to write libraries to other GC'd languages. In Rust all of this is very easy, and you can get the speed bump to your Ruby/Python/JavaScript libraries using a modern and safe language.
Is the speed bump for other-language libraries or for other-language applications?
For speeding up other-language libraries, D has a -betterC mode, which prevents you from using the subset of the language and the libraries (standard & user-defined) that relies on GC. The remaining language is a very clean C that simply works on the other language's GC'd memory (using the other language's C interface), and can use stack allocation or any heap allocation strategy of your choice for its working set (reference counting ala C++ shared_ptr could be the obvious choice, but it is your party).
For other language applications, it is a valid option to speed up the entire application by writing it in D, as it has "all" the features of those other languages + all the convenience that is afforded by a GC + threads if you don't want a multi-process design. I quote "all" because I mean useful things like blocks/closures, generic data structures, etc. - of course, neither Rust nor D give you runtime devices like monkey-patching/meta-class hackery/prototype changes.
For speeding up other-language libraries, D has a -betterC mode, which prevents you from using the subset of the language and the libraries (standard & user-defined) that relies on GC. The remaining language is a very clean C that simply works on the other language's GC'd memory (using the other language's C interface), and can use stack allocation or any heap allocation strategy of your choice for its working set (reference counting ala C++ shared_ptr could be the obvious choice, but it is your party).
For other language applications, it is a valid option to speed up the entire application by writing it in D, as it has "all" the features of those other languages + all the convenience that is afforded by a GC + threads if you don't want a multi-process design. I quote "all" because I mean useful things like blocks/closures, generic data structures, etc. - of course, neither Rust nor D give you runtime devices like monkey-patching/meta-class hackery/prototype changes.