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// =============================================================================
// Copyright (c) 2026 Haixing Hu.
//
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0.
// =============================================================================
use crateByteOutput;
use crateSeekableOutput;
/// A synchronous output that transfers and seeks in bytes.
///
/// This trait adds no methods. Every [`SeekableOutput`] with both
/// `Item = u8` and `Unit = u8`, including unsized streams, implements it
/// automatically. Implement the underlying output and seek traits instead.
///
/// # Examples
/// A byte cursor can be written and repositioned through the trait object:
///
/// ```
/// use std::io::{Cursor, Result, SeekFrom};
/// use qubit_io::SeekableByteOutput;
/// fn rewind(stream: &mut dyn SeekableByteOutput) -> Result<u64> { stream.seek_to(SeekFrom::Start(0)) }
/// let mut cursor = Cursor::new(Vec::<u8>::new());
/// let stream: &mut dyn SeekableByteOutput = &mut cursor;
/// stream.write_fully(b"QBIT")?;
/// assert_eq!(stream.seek_to(SeekFrom::Current(0))?, 4);
/// assert_eq!(rewind(stream)?, 0);
/// stream.write_fully(b"R")?;
/// assert_eq!(cursor.into_inner(), b"RBIT");
/// # Ok::<(), std::io::Error>(())
/// ```
/// Streams with a different item type do not satisfy this bound:
///
/// ```compile_fail
/// use qubit_io::{SeekableByteOutput, SeekableOutput};
///
/// fn accept(stream: impl SeekableByteOutput) {}
///
/// fn reject(stream: impl SeekableOutput<Item = char, Unit = char>) {
/// accept(stream);
/// }
/// ```
///
/// The seek unit must also match the transferred items:
///
/// ```compile_fail
/// use qubit_io::{Output, Seekable, SeekableByteOutput};
///
/// fn accept(stream: impl SeekableByteOutput) {}
///
/// fn reject(stream: impl Output<Item = u8> + Seekable<Unit = char>) {
/// accept(stream);
/// }
/// ```