Make unique identifiers.
[dependencies]
id = "0.1"#[macro_use]externcrate id;
...let x = id!();Each ID identifies a unique point in the source code, so you can't make more of them at runtime with a loop, nor with other such shenanigans.
Just take the code and do whatever you want with it, which I assume isn't much, because this library is pretty much useless.