Re: [RFC PATCH 1/2] rust: LED abstraction

[Marek Behún]

On Wed, Oct 09, 2024 at 12:57:58PM +0200, Fiona Behrens wrote:

> +/// Color of an LED.
> +#[derive(Copy, Clone)]
> +pub enum Color {
> +    /// White
> +    White,
> +    /// Red
> +    Red,
> +    /// Green
> +    Green,
> +    /// Blue
> +    Blue,
> +    /// Amber
> +    Amber,
> +    /// Violet
> +    Violet,
> +    /// Yellow
> +    Yellow,
> +    /// Purple
> +    Purple,
> +    /// Orange
> +    Orange,
> +    /// Pink
> +    Pink,
> +    /// Cyan
> +    Cyan,
> +    /// Lime
> +    Lime,

Why these repetitions?

> +impl TryFrom<u32> for Color {
> +    type Error = Error;
> +
> +    fn try_from(value: u32) -> Result<Self, Self::Error> {
> +        Ok(match value {
> +            bindings::LED_COLOR_ID_WHITE => Color::White,
> +            bindings::LED_COLOR_ID_RED => Color::Red,
> +            bindings::LED_COLOR_ID_GREEN => Color::Green,
> +            bindings::LED_COLOR_ID_BLUE => Color::Blue,
> +            bindings::LED_COLOR_ID_AMBER => Color::Amber,
> +            bindings::LED_COLOR_ID_VIOLET => Color::Violet,
> +            bindings::LED_COLOR_ID_YELLOW => Color::Yellow,
> +            bindings::LED_COLOR_ID_PURPLE => Color::Purple,
> +            bindings::LED_COLOR_ID_ORANGE => Color::Orange,
> +            bindings::LED_COLOR_ID_PINK => Color::Pink,
> +            bindings::LED_COLOR_ID_CYAN => Color::Cyan,
> +            bindings::LED_COLOR_ID_LIME => Color::Lime,
> +            bindings::LED_COLOR_ID_IR => Color::IR,
> +            bindings::LED_COLOR_ID_MULTI => Color::Multi,
> +            bindings::LED_COLOR_ID_RGB => Color::RGB,
> +            _ => return Err(EINVAL),
> +        })
> +    }
> +}

How does Rust compile these? If these constants compile to the same
numeric values, i.e. if
  LED_COLOR_ID_AMBER == Color::Amber,
will the compiler compile away the function?

How do enums work in Rust?

> +impl<'a, T> Led<T>

offtopic, what is 'a ? What does the ' mean? Is impl<> something like
template in c++?

> +where
> +    T: Operations + 'a,

What does + mean here?

> +/// LED brightness.
> +#[derive(Debug, Copy, Clone)]
> +pub enum Brightness {
> +    /// LED off.
> +    Off,
> +    /// Led set to the given value.
> +    On(NonZeroU8),
> +}
> +
> +impl Brightness {
> +    /// Half LED brightness
> +    // SAFETY: constant value non zero
> +    pub const HALF: Self = Self::On(unsafe { NonZeroU8::new_unchecked(127) });
> +    /// Full LED brightness.
> +    pub const FULL: Self = Self::On(NonZeroU8::MAX);

These LED_OFF, LED_ON, LED_HALF and LED_FULL are deprecated constants
that should not be used anymore. enum led_brightness will be either
uint8_t or usigned int in the future.

Is it possible to not infect Rust with these deprecated constants?

Marek