config-pattern.rs

#[derive(Debug)]
struct User {
    name: String,
    email: String,
    sign_in_count: u64,
    active: bool,
}

impl Default for User {
    fn default() -> Self {
        User {
            name: "ahmed".to_owned(),
            email: "ahmed@gmail.com".to_owned(),
            sign_in_count: 0,
            active: false
        }
    }
}

#[derive(Debug)]
enum Direction {
    Horizontal,
    Vertical
}

#[derive(Debug)]
enum Constraint {
    Percentage(u32),
    Min(u32),
    Max(u32)
}

#[derive(Debug)]
struct Layout {
    direction: Direction,
    constraints: Vec<Constraint>,
}

impl Default for Layout {
    fn default() -> Self {
        Layout {
            direction: Direction::Vertical,
            constraints: vec![]
        }
    }
}

macro_rules! config {
    ($t: ident; $($p: ident = $v: expr),*) => {{
        let mut obj: $t = Default::default();
        $(obj.$p = $v;)*
        obj
    }}
}

fn main() {
    let a = User { active: false, sign_in_count: 9, ..User::default() };
    let b = config!(User; sign_in_count=5, active=true, name="ali".to_owned());
    let c = config!(
        Layout;
        direction=Direction::Vertical,
        constraints=vec![Constraint::Percentage(4), Constraint::Percentage(6)]
    );
  
    println!("{:?}", a);
    println!("{:?}", b);
    println!("{:?}", c);
}