Trait mz_ore::fmt::FormatBuffer

pub trait FormatBuffer: AsRef<[u8]> {
    // Required methods
    fn write_fmt(&mut self, fmt: Arguments<'_>);
    fn write_char(&mut self, c: char);
    fn write_str(&mut self, s: &str);
    fn len(&self) -> usize;
    unsafe fn as_bytes_mut(&mut self) -> &mut [u8] ;

    // Provided method
    fn is_empty(&self) -> bool { ... }
}

A trait for objects that can be infallibly written to.

Like std::fmt::Write, except that the methods do not return errors. Implementations are provided for String, bytes::BytesMut, and Vec<u8>, as writing to these types cannot fail.

Objects that implement FormatBuffer can be passed to the write! macro:

use mz_ore::fmt::FormatBuffer;

let mut buf = String::new();
write!(buf, "{:.02}", 1.0 / 7.0);
assert_eq!(buf, "0.14");

The trait is particularly useful for functions that need to generically write to either a String or a byte buffer:

use mz_ore::fmt::FormatBuffer;

fn write_timezone_offset<F>(buf: &mut F, mut offset_seconds: i32)
where
    F: FormatBuffer,
{
    if offset_seconds >= 0 {
        buf.write_char('+');
    } else {
        buf.write_char('-');
    }
    let offset_seconds = offset_seconds.abs();
    write!(buf, "{:02}:{:02}", offset_seconds / 60 / 60, offset_seconds / 60 % 60);
}

let offset_seconds = -18000;

let mut s = String::new();
write_timezone_offset(&mut s, offset_seconds);

let mut v = Vec::new();
write_timezone_offset(&mut v, offset_seconds);

assert_eq!(s, "-05:00");
assert_eq!(v, s.as_bytes());

The implementations of FormatBuffer for Vec<u8> and BytesMut are guaranteed to only write valid UTF-8 bytes into the underlying buffer.

Required Methods

fn write_fmt(&mut self, fmt: Arguments<'_>)

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

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

fn write_char(&mut self, c: char)

Writes a char into this buffer.

fn write_str(&mut self, s: &str)

Writes a string into this buffer.

fn len(&self) -> usize

Returns the number of bytes in the buffer.

unsafe fn as_bytes_mut(&mut self) -> &mut [u8]

Returns a mutable reference to the bytes in the buffer.

Safety

If the byte slice was valid UTF-8, it must remain valid UTF-8 when the Strings or other data types whose memory safety depends upon only containing valid UTF-8.

Provided Methods

fn is_empty(&self) -> bool

Reports whether the buffer is empty.

Implementations on Foreign Types

impl FormatBuffer for BytesMut

fn write_fmt(&mut self, fmt: Arguments<'_>)

fn write_char(&mut self, c: char)

fn write_str(&mut self, s: &str)

fn len(&self) -> usize

unsafe fn as_bytes_mut(&mut self) -> &mut [u8]

impl FormatBuffer for String

fn write_fmt(&mut self, fmt: Arguments<'_>)

fn write_char(&mut self, c: char)

fn write_str(&mut self, s: &str)

fn len(&self) -> usize

unsafe fn as_bytes_mut(&mut self) -> &mut [u8]

impl FormatBuffer for Vec<u8>

fn write_fmt(&mut self, fmt: Arguments<'_>)

fn write_char(&mut self, c: char)

fn write_str(&mut self, s: &str)

fn len(&self) -> usize

unsafe fn as_bytes_mut(&mut self) -> &mut [u8]

Implementors