Enum Never

Source
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§

Source§

impl Never

Source

pub fn into_any<T>(self) -> T

Convert this Never into a value of a different type.

Since a Never can never be constructed, this is valid for any Sized type.

Source

pub fn to_any<T>(&self) -> T

Convert this Never into a value of a different type.

Since a Never can never be constructed, this is valid for any Sized type.

Trait Implementations§

Source§

impl<T: ?Sized> AsMut<T> for Never

Source§

fn as_mut(&mut self) -> &mut T

Converts this type into a mutable reference of the (usually inferred) input type.
Source§

impl<T: ?Sized> AsRef<T> for Never

Source§

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.
Source§

impl BufRead for Never

Source§

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 more
Source§

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 more
Source§

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 more
1.0.0 · Source§

fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes into buf until the delimiter byte or EOF is reached. Read more
1.83.0 · Source§

fn skip_until(&mut self, byte: u8) -> Result<usize, Error>

Skips all bytes until the delimiter byte or EOF is reached. Read more
1.0.0 · Source§

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 more
1.0.0 · Source§

fn split(self, byte: u8) -> Split<Self>
where Self: Sized,

Returns an iterator over the contents of this reader split on the byte byte. Read more
1.0.0 · Source§

fn lines(self) -> Lines<Self>
where Self: Sized,

Returns an iterator over the lines of this reader. Read more
Source§

impl Clone for Never

Source§

fn clone(&self) -> Never

Returns a copy of the value. Read more
1.0.0 · Source§

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
Source§

impl Debug for Never

Source§

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

Formats the value using the given formatter. Read more
Source§

impl Display for Never

Source§

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

Formats the value using the given formatter. Read more
Source§

impl Error for Never

1.30.0 · Source§

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

👎Deprecated since 1.42.0: use the Display impl or to_string()
1.0.0 · Source§

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
Source§

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)
Provides type-based access to context intended for error reports. Read more
Source§

impl Hash for Never

Source§

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more
1.3.0 · Source§

fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
Source§

impl Ord for Never

Source§

fn cmp(&self, other: &Never) -> Ordering

This method returns an Ordering between self and other. Read more
1.21.0 · Source§

fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · Source§

fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · Source§

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized,

Restrict a value to a certain interval. Read more
Source§

impl PartialEq for Never

Source§

fn eq(&self, other: &Never) -> bool

Tests for self and other values to be equal, and is used by ==.
1.0.0 · Source§

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

impl PartialOrd for Never

Source§

fn partial_cmp(&self, other: &Never) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
1.0.0 · Source§

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator. Read more
1.0.0 · Source§

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator. Read more
1.0.0 · Source§

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator. Read more
1.0.0 · Source§

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator. Read more
Source§

impl Read for Never

Source§

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>

Like read, except that it reads into a slice of buffers. Read more
Source§

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)
Determines if this Reader has an efficient read_vectored implementation. Read more
1.0.0 · Source§

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 more
1.0.0 · Source§

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 more
1.6.0 · Source§

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

Reads the exact number of bytes required to fill buf. Read more
Source§

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>

🔬This is a nightly-only experimental API. (read_buf)
Reads the exact number of bytes required to fill cursor. Read more
1.0.0 · Source§

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

Creates a “by reference” adaptor for this instance of Read. Read more
1.0.0 · Source§

fn bytes(self) -> Bytes<Self>
where Self: Sized,

Transforms this Read instance to an Iterator over its bytes. Read more
1.0.0 · Source§

fn chain<R>(self, next: R) -> Chain<Self, R>
where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another. Read more
1.0.0 · Source§

fn take(self, limit: u64) -> Take<Self>
where Self: Sized,

Creates an adapter which will read at most limit bytes from it. Read more
Source§

impl Seek for Never

Source§

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>

Rewind to the beginning of a stream. Read more
Source§

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
1.51.0 · Source§

fn stream_position(&mut self) -> Result<u64, Error>

Returns the current seek position from the start of the stream. Read more
1.80.0 · Source§

fn seek_relative(&mut self, offset: i64) -> Result<(), Error>

Seeks relative to the current position. Read more
Source§

impl Write for Never

Source§

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<()>

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
1.36.0 · Source§

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

Like write, except that it writes from a slice of buffers. Read more
Source§

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)
Determines if this Writer has an efficient write_vectored implementation. Read more
1.0.0 · Source§

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>

🔬This is a nightly-only experimental API. (write_all_vectored)
Attempts to write multiple buffers into this writer. Read more
1.0.0 · Source§

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

Writes a formatted string into this writer, returning any error encountered. Read more
1.0.0 · Source§

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

Creates a “by reference” adapter for this instance of Write. Read more
Source§

impl Copy for Never

Source§

impl Eq for Never

Source§

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> Any for T
where T: 'static + ?Sized,

Source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
Source§

impl<T> Borrow<T> for T
where T: ?Sized,

Source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
Source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

Source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
Source§

impl<T> CloneToUninit for T
where T: Clone,

Source§

unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dest. Read more
Source§

impl<T> From<T> for T

Source§

fn from(t: T) -> T

Returns the argument unchanged.

Source§

impl<T, U> Into<U> for T
where U: From<T>,

Source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

Source§

impl<T> ToOwned for T
where T: Clone,

Source§

type Owned = T

The resulting type after obtaining ownership.
Source§

fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
Source§

fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
Source§

impl<T> ToString for T
where T: Display + ?Sized,

Source§

fn to_string(&self) -> String

Converts the given value to a String. Read more
Source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

Source§

type Error = Infallible

The type returned in the event of a conversion error.
Source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
Source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

Source§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
Source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.