Background

rustc 1.59.0

When Learning to use "rand" I tend to end up in a loop of frustration that I must address.
In my quest as a (rust) newbie I tried following the code snippets in your book , I end up with "failed to resolve" at times :

Rand Book

StdGen snippets works fine,
But how do I "use" SmallRng or ChaCha20Rng, usually "failed to resolve" no matter what I try.

I seems my Cargo.toml / dependencies is missing something, or is it the sample snippet missing "use" ?
How many dependencies (with options) do I need for each sample snippet.. could this be more specific perhaps?