It's hard to measure productivity, but one thing I'd like to point out about Go is that is has relatively few productivity feature. It's main advantage is that's simple, but with automatic derivation, traits, closures, real enums (sum types), Rust actually provides more high level niceties than Go. We can also encode rules using the richer type system of Rust over Go or C++, things like state changes can be verified at compile time via phantom type for example. Expression based programming coupled with the borrow checker allows us to write expressive code that is also efficient.

I'm not going to claim that we have proof the Rust is more productive than Go or C++. I see some concrete advantages, however, Rust may simply better suited to the work we're doing. We might just enjoy writing it and therefore work faster.

The way I see it is that Rust guides you to better architectures, it offers a lot of very powerful features from FP and PL theory, and it's all engineered to make sense as a language. In that way, I think it's similar to Go in that they're both engineered while C++ has a lot of fossilized layers and has been organically grown for decades now. We have C++ code from half a decade ago that looks nothing like what we are writing now. It's this organic beast that has a lot of baggage. Rust and Go are engineered from the ground up, and with Rust editions I think they will avoid becoming the organic beast that C++ is now.

It probably depends greatly on what you are doing. There is a lot of work where I would be much more productive in Go because I have yet to really master Rust, as it is a big and complex language while Go is so simple. But I have also made a library where the various meta-programming features in Rust saved me thousands of hours of work and ongoing maintenance compared to what it would have taken to recreate it in Go.

Similarly, the productivity difference will depend on how much run-time performance you need. It might be take longer to make Go code very fast if you need very fast. Having to work around the garbage collector, and avoiding interface {} etc.

> We have C++ code from half a decade ago that looks nothing like what we are writing now.

well, Rust code from half a decade ago is also somewhat distinct from today's rust.. even basic cases don't compile anymore : http://progopedia.com/language/rust/

Half a decade ago, Rust 1.0 didn't exist. The language was explicitly unstable.