Logic behind an allergies test

[andrey-gvrd]

@adolfosilva

What is the logic behind this test?

#[test]
fn test_ignore_non_allergen_score_parts() {
    assert_eq!(vec![Allergen::Eggs], Allergies(257).allergies());
}

I'd understand if this test expected an empty vector since the score cannot be constructed out of a sum of Allergen values, by I can't figure out why Allergen::Eggs are expected to get through.

[adolfosilva]

I don't quite remember what this test was supposed to do due to lack of documentation and from being a translation from some other language.

The score can be the sum of all the Allergen index values (starting at 1) which would be equal to 255 and that test is covered. With a value of 257, we get a result that's essentially Allergies(1) (256 counts as 0). Allergies(258) would be Allergies(2) and so on...

Sorry that i can't be of more help than this.

[andrey-gvrd]

That would make sense if your system's usize was 8 bits)

[kytrinyx]

The idea behind this exercise was to introduce the idea of bitmasks. Beyond that I can't remember the details.

[andrey-gvrd]

Wow, that part went completely over my head.