qubit-io 0.9.0

Byte-stream buffering and std::io utilities for Rust
Documentation 
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// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================

use std::io::{
    Result,
    Seek,
    SeekFrom,
};

/// Minimal seek interface measured in stream units.
///
/// Unlike [`Seek`], which measures positions and offsets in bytes,
/// `Seekable` measures them in units of [`Self::Item`]. For byte streams,
/// set `Item = u8`; offsets passed through [`SeekFrom`] then count units
/// rather than bytes.
///
/// The return value of [`Seekable::seek`] is the new absolute position from
/// the start of the stream, in units.
///
/// # Coherence note
///
/// The blanket impl below maps [`std::io::Seek`] to `Item = u8` for binary
/// compatibility. If a concrete type already implements `Seek`, it already has
/// an implicit `Seekable<Item = u8>` impl from this blanket, so another
/// `Seekable` impl with the same `(Self, Item)` pair would be a coherence
/// conflict.
///
/// For example, this is rejected by the compiler:
///
/// ```rust,compile_fail
/// use std::io::{Result, Seek, SeekFrom};
///
/// struct LegacyStream;
///
/// impl Seek for LegacyStream {
///     fn seek(&mut self, _pos: SeekFrom) -> Result<u64> {
///         Ok(0)
///     }
/// }
///
/// impl crate::Seekable for LegacyStream {
///     type Item = u8;
///     fn seek(&mut self, _pos: SeekFrom) -> Result<u64> {
///         Ok(0)
///     }
/// }
/// ```
///
/// ```text
/// error[E0119]: conflicting implementations of trait `crate::Seekable`
/// for type `LegacyStream`
/// ```
///
/// The stable workaround is to keep byte-positioned seeking on the original
/// type and introduce a wrapper/newtype when another unit interpretation is
/// needed: implement `Seekable` for the wrapper with a different `Item`, and
/// keep `std::io::Seek`/byte semantics on the original type.
pub trait Seekable {
    /// The unit type used to measure seek positions and offsets.
    type Item;

    /// Seeks to a position in the stream.
    ///
    /// # Parameters
    ///
    /// * `position` - Target position relative to the start, end, or current
    ///   logical position. All offsets are counted in units of [`Self::Item`].
    ///
    /// # Returns
    ///
    /// The new absolute stream position, in units.
    ///
    /// # Errors
    ///
    /// Returns the seek error reported by the implementation.
    fn seek(&mut self, position: SeekFrom) -> Result<u64>;
}

impl<S> Seekable for S
where
    S: Seek + ?Sized,
{
    type Item = u8;

    /// Seeks a standard [`Seek`] value using byte offsets.
    #[inline(always)]
    fn seek(&mut self, position: SeekFrom) -> Result<u64> {
        Seek::seek(self, position)
    }
}