breakpoints!

breakpoints.rs

// ------Seed code ------

#[derive(Debug)]
struct BreakpointInterval<B> {
    id: B,
    start: u32,
    end: Option<u32>,
}

#[derive(Debug)]
struct Theme<B> {
    id: String,
    breakpoints: Vec<BreakpointInterval<B>>,
    breakpoint_scale: Vec<u32>,
}
impl<B> Theme<B> {
    fn new(id: impl ToString) -> Self {
        Self {
            id: id.to_string(),
            breakpoints: Vec::new(),
            breakpoint_scale: Vec::new(),
        }
    }
    fn set_breakpoints(mut self, breakpoints: Vec<BreakpointInterval<B>>) -> Self {
        self.breakpoint_scale = breakpoints.iter().skip(1).map(|interval| interval.start).collect();
        self.breakpoints = breakpoints;
        self
    }
}

macro_rules! breakpoints {
    { $($num:expr, $id:expr $(,)?)* } => {
        {
            let mut nums = Vec::new();
            let mut ids = Vec::new();
            $(
                nums.push($num);
                ids.push($id);
            )*
            breakpoint_intervals(nums, ids)
        }
    } 
}

fn breakpoint_intervals<B>(nums: Vec<u32>, ids: Vec<B>) -> Vec<BreakpointInterval<B>> {
    ids.into_iter().enumerate().map(|(index, id)| {
        BreakpointInterval {
            id,
            start: nums[index],
            end: nums.get(index+1).copied(),
        }
    }).collect()
}

// ------App code ------

#[derive(Debug)]
enum Breakpoint {
    ExtraSmall,
    Small,
    Medium,
    Large,
    ExtraLarge,
}

fn main() {
    use Breakpoint::*;
    let theme = Theme::new("my_theme").set_breakpoints(breakpoints![
        0, ExtraSmall, 600, Small, 960, Medium, 1280, Large, 1920, ExtraLarge
    ]);
    println!("{:#?}", theme);
}

Runnable in https://play.rust-lang.org/