I'm hopeful that Rust will lead in a good direction. A C-style ABI, by virtue of being the least common denominator, is probably the best bet for re-usability

I'm hopeful that Rust will lead in a good direction. A C-style ABI, by virtue of being the least common denominator, is probably the best bet for re-usability across paradigms. Higher level languages would want to write idiomatic façades, but they already habitually do that anyway, even on higher-level platforms like Java and .NET. And I think that deterministic memory management is probably also a pretty important feature. You don't want your libraries all bringing their own clever ideas about object lifetimes and such. But you also need it to be very reliable; a real danger with inviting libraries written in C and C++ into your process space is that they are liable to corrupt your memory. Rust's affine type system seems like a big step in the right direction here. Similar thoughts for the error model. I don't have any particular complaints about exceptions, except that you don't want to be bleeding them on an external API, because that ends up being another spot where languages can fail to mesh. What's missing, though, is that there is no good cross-platform standard for libraries that work with the C ABI (neither in source nor binary form) for other languages to plug into. So that's where I get to thinking that Rust might be closer to (if not exactly at) the mark than C is.