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//! Extension traits.
use core::fmt::{Alignment, Arguments, Formatter, Result, Write};
mod sealed {
pub trait Sealed {}
impl Sealed for core::fmt::Formatter<'_> {}
}
/// An extension trait for [`core::fmt::Formatter`].
pub trait FormatterExt: sealed::Sealed {
/// Writes the given arguments to the formatter, padding them with the given width. If `width`
/// is incorrect, the resulting output will not be the requested width.
fn pad_with_width(&mut self, width: usize, args: Arguments<'_>) -> Result;
}
impl FormatterExt for Formatter<'_> {
fn pad_with_width(&mut self, args_width: usize, args: Arguments<'_>) -> Result {
let Some(final_width) = self.width() else {
// The caller has not requested a width. Write the arguments as-is.
return self.write_fmt(args);
};
let Some(fill_width @ 1..) = final_width.checked_sub(args_width) else {
// No padding will be present. Write the arguments as-is.
return self.write_fmt(args);
};
let alignment = self.align().unwrap_or(Alignment::Left);
let fill = self.fill();
let left_fill_width = match alignment {
Alignment::Left => 0,
Alignment::Right => fill_width,
Alignment::Center => fill_width / 2,
};
let right_fill_width = match alignment {
Alignment::Left => fill_width,
Alignment::Right => 0,
// When the fill is not even on both sides, the extra fill goes on the right.
Alignment::Center => (fill_width + 1) / 2,
};
for _ in 0..left_fill_width {
self.write_char(fill)?;
}
self.write_fmt(args)?;
for _ in 0..right_fill_width {
self.write_char(fill)?;
}
Ok(())
}
}