Write in std::fmt - Rust (original) (raw)

Trait std::fmt::Write

1.0.0· source · [−]

Expand description

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.

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.

This function will return an instance of Error on error.

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");

Run

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.

This function will return an instance of Error on error.

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");

Run

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.

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");

Run