Before doing this exercise you should probably do the original Luhn exercise and its successor, "Luhn: Using the From Trait"
To get the original Luhn exercise, run
exercism download --exercise=luhn --track=rust
To get the "Luhn: Using the From Trait" exercise, run
exercism download --exercise=luhn-from --track=rust
In the original Luhn exercise you only validated strings, but the Luhn algorithm can be applied to integers as well.
In "Luhn: Using the From Trait" you implemented a From trait, which also required you to create a Luhn struct.
Instead of creating a Struct just to perform the validation, what if you validated the primitives (i.e, String, u8, etc.) themselves?
In this exercise you'll create and implement a custom trait that performs the validation.