core::fmt

Trait LowerExp

1.6.0 · Source

pub trait LowerExp: PointeeSized {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

Expand description

e formatting.

The LowerExp trait should format its output in scientific notation with a lower-case e.

For more information on formatters, see the module-level documentation.

§Examples

Basic usage with f64:

let x = 42.0; // 42.0 is '4.2e1' in scientific notation

assert_eq!(format!("{x:e}"), "4.2e1");

Implementing LowerExp on a type:

use std::fmt;

struct Length(i32);

impl fmt::LowerExp for Length {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let val = f64::from(self.0);
        fmt::LowerExp::fmt(&val, f) // delegate to f64's implementation
    }
}

let l = Length(100);

assert_eq!(
    format!("l in scientific notation is: {l:e}"),
    "l in scientific notation is: 1e2"
);

assert_eq!(
    format!("l in scientific notation is: {l:05e}"),
    "l in scientific notation is: 001e2"
);

Required Methods§

1.0.0 · Source

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

§Errors

This function should return Err if, and only if, the provided Formatter returns Err. String formatting is considered an infallible operation; this function only returns a Result because writing to the underlying stream might fail and it must provide a way to propagate the fact that an error has occurred back up the stack.