When writing one of my pet projects or rather, a very simple automation matter in Rust, I fell into many pits. Usually full of snakes (of my own lack of knowledge of rust), but this one struck me as relatively interesting.
The stable compiler does not allow you to use unstable APIs/features. You have to use the nightly release branch.
If you know node, this is probably the equivalent of having to run V8 with harmony flags.
Rustup easily enables you to install the nightly branch of rust and to use it by default: