Hands-on Rust: RGB:named(...) not necessary?

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My goodness, you’re right. That’s somewhat embarrassing on my end. It looks like I can get rid of the RGB::named and just use the constants. (I just changed a few at random and everything still works; I’ll get this updated for the next beta). Thank you for that - it makes the code look a LOT nicer.

Some history for how I improved that without realizing I’d fixed it.

Early in bracket-lib development, the color constants were all defined as tuple triplets. For example:

pub const BISQUE: (u8, u8, u8) = (255, 228, 196);

I thought that was a bit unwieldy, because RGB back then was pretty dumb and wouldn’t work without the named constructor. I implemented the From trait for RGB, allowing it to be constructed with RGB::from(NAMED_COLOR) or NAMED_COLOR.into(). That was a bit better, and more Rusty.

Anyway, a while later the terminal gained support for alpha transparency. Suddenly, I needed RGBA and not RGB everywhere! So all of the terminal functions became generic parameters accepting any type of TryInto<RGBA> - and conversion was added for RGB <-> RGBA. That was great, because you could use whichever one suited your problem domain and it would convert between them.

Using Into and TryInto gets a little complex, but it works remarkably well. The function signature for set is as follows:

pub fn set<COLOR, COLOR2, GLYPH, X, Y>(
        &mut self,
        x: X,
        y: Y,
        fg: COLOR,
        bg: COLOR2,
        glyph: GLYPH,
    ) where
        COLOR: Into<RGBA>,
        COLOR2: Into<RGBA>,
        GLYPH: TryInto<FontCharType>,
        X: TryInto<i32>,
        Y: TryInto<i32>,
    {

See how it uses generics (like you do for Vec<T>) with an additional where constraint? The color fields will accept anything that knows how to convert into an RGBA type. (When you implement From you get Into for free - one of the few times Rust isn’t explicit). So what’s with the TryInto? I wanted the user to be able to type any type of number they wanted, rather than having to remember that x is an i32 and so on. Not all numbers are readily convertible - and some numbers may be converted for some values and not others. For example, converting a signed integer into an unsigned integer doesn’t make sense for a negative number. TryInto attempts the conversion and throws an error our if the conversion fails at runtime.

It seriously never occurred to me that because RGB/RGBA have From<(u8, u8, u8)> defined it now automatically accepted the color constants.

So thank you! I learned something and the book code will be easier to read. :slight_smile:

(Edit: I should add that using traits and making your own is planned for the next beta. They are remarkably powerful)

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