[Manishearth]

Right, like I said, this particular feature exists in a million languages. I'm talking about the whole set of features that Rust has; some are from research languages and may have never been seen in the industry before (e.g. regions/borrow checking), but they're not really new. This particular feature in Rust descended from the ML family (since Rust used to be ML-like), which in turn probably got it from Ada or w/e.

[nv-vn]

ML predates Ada by about 7 years, so that's unlikely. The way it is implemented in ML is most likely just an implementation of the mathematical concept of sum types rather than a feature influenced by existing programming languages.

[Manishearth]

> ML predates Ada by about 7 years, so that's unlikely.

Ha! I didn't know that. Thanks :)