Trait std::fmt::LowerExp

e 格式。

LowerExp trait 应该使用小写的 e 以科学计数法格式化其输出。

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

f64 的基本用法：

let x = 42.0; // 42.0 是 '4.2e1' 的科学计数形式

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

在类型上实现 LowerExp：

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) // 委托 f64 的实现
    }
}

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

fmt

使用给定的格式化程序格式化该值。

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

Implementors

impl LowerExp for f32

impl LowerExp for f64

impl LowerExp for i8

impl LowerExp for i16

impl LowerExp for i32

impl LowerExp for i64

impl LowerExp for i128

impl LowerExp for isize

impl LowerExp for u8

impl LowerExp for u16

impl LowerExp for u32

impl LowerExp for u64

impl LowerExp for u128

impl LowerExp for usize

impl<T> LowerExp for &T

impl<T> LowerExp for &T
where
  T: LowerExp + ?Sized,

impl<T> LowerExp for &mut T

impl<T> LowerExp for &mut T
where
  T: LowerExp + ?Sized,