Feature gate: #![feature(bufwriter_into_parts)]

This is a tracking issue for BufWriter::into_parts and its associated error type etc.

This allows a BufWriter to be disassembled, and the inner writer to be recovered - without attempting to write out any buffered data (instead it is returnedt to the caller), and therefore (unlike into_inner) succeeding even if the underlying writer is returning errors.

Public API

// std::io

/// Disassembles this `BufWriter<W>`, returning the underlying writer, and any buffered but
/// unwritten data.
impl<W> BufWriter<W> {
    pub fn into_parts(mut self) -> (W, Result<Vec<u8>, WriterPanicked>);
}

/// Error newtype, wraps the buffered data, a `Vec<u8>`
pub struct WriterPanicked {...}

impl WriterPanicked {
    pub fn into_inner(self) -> Vec<u8>;
}

impl Error for WriterPanicked {...}
impl Display for WriterPanicked {...}
impl Debug for WriterPanicked {...}

Steps / History

• Implementation: BufWriter: Provide into_raw_parts #79705
• Gain experience with this API, to see if it's good
• Stabilization PR with Final commenting period (FCP)

Unresolved Questions

• Should into_raw_parts be called into_parts? Tracking Issue for BufWriter::into_parts #80690 (comment)
• Is there a suitable simpler API for presenting this functionality? (I think not, see BufWriter: Provide into_raw_parts #79705 (comment))