Implemented by complex types that don't require any additional context to build themselves to a writer

Example

use std::io::{Cursor, Read};
use bitstream_io::{BigEndian, BitWrite, BitWriter, ToBitStream};

#[derive(Debug, PartialEq, Eq)]
struct BlockHeader {
    last_block: bool,
    block_type: u8,
    block_size: u32,
}

impl ToBitStream for BlockHeader {
    type Error = std::io::Error;

    fn to_writer<W: BitWrite + ?Sized>(&self, w: &mut W) -> std::io::Result<()> {
        w.write_bit(self.last_block)?;
        w.write(7, self.block_type)?;
        w.write(24, self.block_size)
    }
}

let mut data = Vec::new();
let mut writer = BitWriter::endian(&mut data, BigEndian);
writer.build(&BlockHeader { last_block: false, block_type: 4, block_size: 122 }).unwrap();
assert_eq!(data, b"\x04\x00\x00\x7A");