Struct std::io::readbuf::BorrowedCursor

pub struct BorrowedCursor<'a> {
    buf: &'a mut BorrowedBuf<'a>,
    start: usize,
}

🔬This is a nightly-only experimental API. (read_buf #78485)

A writeable view of the unfilled portion of a BorrowedBuf.

Provides access to the initialized and uninitialized parts of the underlying BorrowedBuf. Data can be written directly to the cursor by using append or indirectly by getting a slice of part or all of the cursor and writing into the slice. In the indirect case, the caller must call advance after writing to inform the cursor how many bytes have been written.

Once data is written to the cursor, it becomes part of the filled portion of the underlying BorrowedBuf and can no longer be accessed or re-written by the cursor. I.e., the cursor tracks the unfilled part of the underlying BorrowedBuf.

The lifetime 'a is a bound on the lifetime of the underlying buffer (which means it is a bound on the data in that buffer by transitivity).

Fields

buf: &'a mut BorrowedBuf<'a>

🔬This is a nightly-only experimental API. (read_buf #78485)

The underlying buffer.

start: usize

🔬This is a nightly-only experimental API. (read_buf #78485)

The length of the filled portion of the underlying buffer at the time of the cursor’s creation.

Implementations

impl<'a> BorrowedCursor<'a>

pub fn reborrow<'this>(&'this mut self) -> BorrowedCursor<'this>

🔬This is a nightly-only experimental API. (read_buf #78485)

Reborrow this cursor by cloning it with a smaller lifetime.

Since a cursor maintains unique access to its underlying buffer, the borrowed cursor is not accessible while the new cursor exists.

pub fn capacity(&self) -> usize

🔬This is a nightly-only experimental API. (read_buf #78485)

Returns the available space in the cursor.

pub fn written(&self) -> usize

🔬This is a nightly-only experimental API. (read_buf #78485)

Returns the number of bytes written to this cursor since it was created from a BorrowedBuf.

Note that if this cursor is a reborrowed clone of another, then the count returned is the count written via either cursor, not the count since the cursor was reborrowed.

pub fn init_ref(&self) -> &[u8]

🔬This is a nightly-only experimental API. (read_buf #78485)

Returns a shared reference to the initialized portion of the cursor.

pub fn init_mut(&mut self) -> &mut [u8]

🔬This is a nightly-only experimental API. (read_buf #78485)

Returns a mutable reference to the initialized portion of the cursor.

pub fn uninit_mut(&mut self) -> &mut [MaybeUninit<u8>]

🔬This is a nightly-only experimental API. (read_buf #78485)

Returns a mutable reference to the uninitialized part of the cursor.

It is safe to uninitialize any of these bytes.

pub unsafe fn as_mut(&mut self) -> &mut [MaybeUninit<u8>]

🔬This is a nightly-only experimental API. (read_buf #78485)

Returns a mutable reference to the whole cursor.

Safety

The caller must not uninitialize any bytes in the initialized portion of the cursor.

pub unsafe fn advance(&mut self, n: usize) -> &mut Self

🔬This is a nightly-only experimental API. (read_buf #78485)

Advance the cursor by asserting that n bytes have been filled.

After advancing, the n bytes are no longer accessible via the cursor and can only be accessed via the underlying buffer. I.e., the buffer’s filled portion grows by n elements and its unfilled portion (and the capacity of this cursor) shrinks by n elements.

Safety

The caller must ensure that the first n bytes of the cursor have been properly initialised.

pub fn ensure_init(&mut self) -> &mut Self

🔬This is a nightly-only experimental API. (read_buf #78485)

Initializes all bytes in the cursor.

pub unsafe fn set_init(&mut self, n: usize) -> &mut Self

🔬This is a nightly-only experimental API. (read_buf #78485)

Asserts that the first n unfilled bytes of the cursor are initialized.

BorrowedBuf assumes that bytes are never de-initialized, so this method does nothing when called with fewer bytes than are already known to be initialized.

Safety

The caller must ensure that the first n bytes of the buffer have already been initialized.

pub fn append(&mut self, buf: &[u8])

🔬This is a nightly-only experimental API. (read_buf #78485)

Appends data to the cursor, advancing position within its buffer.

Panics

Panics if self.capacity() is less than buf.len().

Trait Implementations

impl<'a> Debug for BorrowedCursor<'a>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'a> Write for BorrowedCursor<'a>

fn write(&mut self, buf: &[u8]) -> Result<usize>

Write a buffer into this writer, returning how many bytes were written.

fn flush(&mut self) -> Result<()>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector #69941)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all(&mut self, buf: &[u8]) -> Result<()>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>

🔬This is a nightly-only experimental API. (write_all_vectored #70436)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Selfwhere Self: Sized,

Creates a “by reference” adapter for this instance of Write.