pub enum Never {}
Expand description
A type that can never be constructed.
Never
can never be constructed (in type theory parlance, it is
“uninhabited”). It represents any computation which never resolves to a
particular value (because it runs forever, panics, aborts the process, etc).
Because the Never
type can never be constructed, the existence of a
Never
proves that a piece of code can never be reached.
For example, we could write a function like:
fn result_into_ok<T>(res: Result<T, Never>) -> T {
match res {
Ok(t) => t,
// This branch can never be taken, and so the
// compiler is happy to treat it as evaluating
// to whatever type we wish - in this case, `T`.
Err(never) => match never {},
}
}
Generalizing, it is always valid to convert a Never
into a value of any
other type. We provide the into_any
and to_any
methods for this
purpose.
Never
is a stable version of the currently-unstable !
type from the
standard library.
Implementations§
Trait Implementations§
Source§impl BufRead for Never
impl BufRead for Never
Source§fn fill_buf(&mut self) -> Result<&[u8]>
fn fill_buf(&mut self) -> Result<&[u8]>
Returns the contents of the internal buffer, filling it with more data, via
Read
methods, if empty. Read moreSource§fn consume(&mut self, _amt: usize)
fn consume(&mut self, _amt: usize)
Marks the given
amount
of additional bytes from the internal buffer as having been read.
Subsequent calls to read
only return bytes that have not been marked as read. Read moreSource§fn has_data_left(&mut self) -> Result<bool, Error>
fn has_data_left(&mut self) -> Result<bool, Error>
🔬This is a nightly-only experimental API. (
buf_read_has_data_left
)Checks if there is any data left to be
read
. Read more1.83.0 · Source§fn skip_until(&mut self, byte: u8) -> Result<usize, Error>
fn skip_until(&mut self, byte: u8) -> Result<usize, Error>
Skips all bytes until the delimiter
byte
or EOF is reached. Read more1.0.0 · Source§fn read_line(&mut self, buf: &mut String) -> Result<usize, Error>
fn read_line(&mut self, buf: &mut String) -> Result<usize, Error>
Reads all bytes until a newline (the
0xA
byte) is reached, and append
them to the provided String
buffer. Read moreSource§impl Error for Never
impl Error for Never
1.30.0 · Source§fn source(&self) -> Option<&(dyn Error + 'static)>
fn source(&self) -> Option<&(dyn Error + 'static)>
Returns the lower-level source of this error, if any. Read more
1.0.0 · Source§fn description(&self) -> &str
fn description(&self) -> &str
👎Deprecated since 1.42.0: use the Display impl or to_string()
Source§impl Ord for Never
impl Ord for Never
Source§impl PartialOrd for Never
impl PartialOrd for Never
Source§impl Read for Never
impl Read for Never
Source§fn read(&mut self, _buf: &mut [u8]) -> Result<usize>
fn read(&mut self, _buf: &mut [u8]) -> Result<usize>
Pull some bytes from this source into the specified buffer, returning
how many bytes were read. Read more
1.36.0 · Source§fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>
Like
read
, except that it reads into a slice of buffers. Read moreSource§fn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
🔬This is a nightly-only experimental API. (
can_vector
)1.0.0 · Source§fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>
Reads all bytes until EOF in this source, placing them into
buf
. Read more1.0.0 · Source§fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>
fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>
Reads all bytes until EOF in this source, appending them to
buf
. Read more1.6.0 · Source§fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>
Reads the exact number of bytes required to fill
buf
. Read moreSource§fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>
fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>
🔬This is a nightly-only experimental API. (
read_buf
)Pull some bytes from this source into the specified buffer. Read more
Source§fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>
🔬This is a nightly-only experimental API. (
read_buf
)Reads the exact number of bytes required to fill
cursor
. Read more1.0.0 · Source§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Creates a “by reference” adaptor for this instance of
Read
. Read moreSource§impl Seek for Never
impl Seek for Never
Source§fn seek(&mut self, _pos: SeekFrom) -> Result<u64>
fn seek(&mut self, _pos: SeekFrom) -> Result<u64>
Seek to an offset, in bytes, in a stream. Read more
1.55.0 · Source§fn rewind(&mut self) -> Result<(), Error>
fn rewind(&mut self) -> Result<(), Error>
Rewind to the beginning of a stream. Read more
Source§fn stream_len(&mut self) -> Result<u64, Error>
fn stream_len(&mut self) -> Result<u64, Error>
🔬This is a nightly-only experimental API. (
seek_stream_len
)Returns the length of this stream (in bytes). Read more
Source§impl Write for Never
impl Write for Never
Source§fn write(&mut self, _buf: &[u8]) -> Result<usize>
fn write(&mut self, _buf: &[u8]) -> Result<usize>
Writes a buffer into this writer, returning how many bytes were written. Read more
Source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
Flushes this output stream, ensuring that all intermediately buffered
contents reach their destination. Read more
Source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
🔬This is a nightly-only experimental API. (
can_vector
)1.0.0 · Source§fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>
fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>
Attempts to write an entire buffer into this writer. Read more
Source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>
🔬This is a nightly-only experimental API. (
write_all_vectored
)Attempts to write multiple buffers into this writer. Read more
impl Copy for Never
impl Eq for Never
impl StructuralPartialEq for Never
Auto Trait Implementations§
impl Freeze for Never
impl RefUnwindSafe for Never
impl Send for Never
impl Sync for Never
impl Unpin for Never
impl UnwindSafe for Never
Blanket Implementations§
Source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
Source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more