Chapter 4: confusement of summation and bitwise OR, _char_index reimplementation

[Centrix14]

Hello! I'm sure you will find useful these small propositions about chapter 4.

First. In sections 4.4.1 and 4.5.2 you suggest using sum (+) to implement bit overlaying. Technically it will work, but semantically it's doubtful. In essence, overlaying is a bitwise OR operation, not summation. Summation may be very confusing for those (who like me) know how sum is implemented in a low-level. Additionally, bitwise OR will be more consistent (since you are introducing bitwise AND) and pedagogically useful (since this project is, in essence, an etude).

Second. In section 4.5.1 you introduce a "brute force" implementation of _char_index function. This is a probable but not appropriate suggestion. From a programmer's view, following code will be faster and, at the same time, more beautiful:

fn _char_at(self: Base64, char: u8) u8 {
    return switch (char) {
        48...57 => char + 4, // char is a digit
        65...90 => char - 65, // char is a capital letter
        97...122 => char - 71, // char is a small letter
        '+' => 62,
        '/' => 63,
        '=' => 64,
        else => unreachable
    };
}

This kind of implementation I used in my own code.

Another reason for this implementation is purely pedagogical nature. In previous chapters you have explained two key points about switches in Zig: (1) they can be expressions, (2) they can use ranges. So why won't apply this knowledge to a real case?

I'm not fighting for the full removal of the "brute force" variant. I think it will be better to show both ways: simple (which is an exercise in loops) and more sophisticated (which requires familiarity with the ASCII table and knowledge of Zig's switch powers).

[pedropark99]

Interesting points you have here 🧐🤔