Trait core::fmt::Write

pub trait Write {
    fn write_str(&mut self, s: &str) -> Result;

    fn write_char(&mut self, c: char) -> Result { ... }
    fn write_fmt(&mut self, args: Arguments<'_>) -> Result { ... }
}

A trait for writing or formatting into Unicode-accepting buffers or streams.

This trait only accepts UTF-8–encoded data and is not flushable. If you only want to accept Unicode and you don’t need flushing, you should implement this trait; otherwise you should implement std::io::Write.

Required Methods

fn write_str(&mut self, s: &str) -> Result

Writes a string slice into this writer, returning whether the write succeeded.

This method can only succeed if the entire string slice was successfully written, and this method will not return until all data has been written or an error occurs.

Errors

This function will return an instance of Error on error.

The purpose of std::fmt::Error is to abort the formatting operation when the underlying destination encounters some error preventing it from accepting more text; it should generally be propagated rather than handled, at least when implementing formatting traits.

Examples

use std::fmt::{Error, Write};

fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
    f.write_str(s)
}

let mut buf = String::new();
writer(&mut buf, "hola").unwrap();
assert_eq!(&buf, "hola");

Provided Methods

fn write_char(&mut self, c: char) -> Result

Writes a char into this writer, returning whether the write succeeded.

A single char may be encoded as more than one byte. This method can only succeed if the entire byte sequence was successfully written, and this method will not return until all data has been written or an error occurs.

Errors

This function will return an instance of Error on error.

Examples

use std::fmt::{Error, Write};

fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
    f.write_char(c)
}

let mut buf = String::new();
writer(&mut buf, 'a').unwrap();
writer(&mut buf, 'b').unwrap();
assert_eq!(&buf, "ab");

fn write_fmt(&mut self, args: Arguments<'_>) -> Result

Glue for usage of the write! macro with implementors of this trait.

This method should generally not be invoked manually, but rather through the write! macro itself.

Examples

use std::fmt::{Error, Write};

fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
    f.write_fmt(format_args!("{s}"))
}

let mut buf = String::new();
writer(&mut buf, "world").unwrap();
assert_eq!(&buf, "world");

Implementors

impl Write for Formatter<'_>

impl<W: Write + ?Sized> Write for &mut W