Trait 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.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementations on Foreign Types

impl FormatBuffer for BytesMut

Available on crate feature network only.

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