マクロルール(macro_rule!)を使って型の定義

Rust

image-rsから

macro_rules! define_colors {
    {$(
        $ident:ident,
        $channels: expr,
        $alphas: expr,
        $interpretation: expr,
        $color_type_u8: expr,
        $color_type_u16: expr,
        #[$doc:meta];
    )*} => {

$( // START Structure definitions

#[$doc]
#[derive(PartialEq, Eq, Clone, Debug, Copy, Hash)]
#[repr(C)]
#[allow(missing_docs)]
pub struct $ident<T: Primitive> (pub [T; $channels]);

impl<T: Primitive + 'static> Pixel for $ident<T> {
    type Subpixel = T;

    const CHANNEL_COUNT: u8 = $channels;

    const COLOR_MODEL: &'static str = $interpretation;

    const COLOR_TYPE: ColorType =
        [$color_type_u8, $color_type_u16][(std::mem::size_of::<T>() > 1) as usize];

    #[inline(always)]
    fn channels(&self) -> &[T] {
        &self.0
    }
    #[inline(always)]
    fn channels_mut(&mut self) -> &mut [T] {
        &mut self.0
    }

    fn channels4(&self) -> (T, T, T, T) {
        const CHANNELS: usize = $channels;
        let mut channels = [T::max_value(); 4];
        channels[0..CHANNELS].copy_from_slice(&self.0);
        (channels[0], channels[1], channels[2], channels[3])
    }

    fn from_channels(a: T, b: T, c: T, d: T,) -> $ident<T> {
        const CHANNELS: usize = $channels;
        *<$ident<T> as Pixel>::from_slice(&[a, b, c, d][..CHANNELS])
    }

....


impl<T: Primitive + 'static> From<[T; $channels]> for $ident<T> {
    fn from(c: [T; $channels]) -> Self {
        Self(c)
    }
}

)* // END Structure definitions

    }
}

define_colors! {
    Rgb, 3, 0, "RGB", ColorType::Rgb8, ColorType::Rgb16, #[doc = "RGB colors"];
    Bgr, 3, 0, "BGR", ColorType::Bgr8, ColorType::Bgr8, #[doc = "BGR colors"];
    Luma, 1, 0, "Y", ColorType::L8, ColorType::L16, #[doc = "Grayscale colors"];
    Rgba, 4, 1, "RGBA", ColorType::Rgba8, ColorType::Rgba16, #[doc = "RGB colors + alpha channel"];
    Bgra, 4, 1, "BGRA", ColorType::Bgra8, ColorType::Bgra8, #[doc = "BGR colors + alpha channel"];
    LumaA, 2, 1, "YA", ColorType::La8, ColorType::La16, #[doc = "Grayscale colors + alpha channel"];
}