Fmt Structs

Formatting types

Formatter

use std::fmt::{self, Formatter};

struct Point {
    x: f64,
    y: f64,
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        // Access formatter options
        if f.alternate() {
            // # flag
            write!(f, "Point {{\n  x: {},\n  y: {}\n}}", self.x, self.y)
        } else if let Some(precision) = f.precision() {
            write!(f, "({:.prec$}, {:.prec$})", self.x, self.y, prec = precision)
        } else {
            write!(f, "({}, {})", self.x, self.y)
        }
    }
}

impl fmt::Debug for Point {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        f.debug_struct("Point")
            .field("x", &self.x)
            .field("y", &self.y)
            .finish()
    }
}

fn main() {
    let p = Point { x: 3.14159, y: 2.71828 };

    // Different format options
    println!("Default: {}", p);
    println!("Alternate: {:#}", p);
    println!("Precision: {:.2}", p);
    println!("Debug: {:?}", p);
    println!("Pretty Debug: {:#?}", p);
}