# Struct heapless::HistoryBuffer

source ·

    pub struct HistoryBuffer<T, const N: usize> { /* private fields */ }

Expand description

A “history buffer”, similar to a write-only ring buffer of fixed length.

This buffer keeps a fixed number of elements. On write, the oldest element is overwritten. Thus, the buffer is useful to keep a history of values with some desired depth, and for example calculate a rolling average.

## Examples

    use heapless::HistoryBuffer;

    // Initialize a new buffer with 8 elements.
    let mut buf = HistoryBuffer::<_, 8>::new();

    // Starts with no data
    assert_eq!(buf.recent(), None);

    buf.write(3);
    buf.write(5);
    buf.extend(&[4, 4]);

    // The most recent written element is a four.
    assert_eq!(buf.recent(), Some(&4));

    // To access all elements in an unspecified order, use `as_slice()`.
    for el in buf.as_slice() { println!("{:?}", el); }

    // Now we can prepare an average of all values, which comes out to 4.
    let avg = buf.as_slice().iter().sum::<usize>() / buf.len();
    assert_eq!(avg, 4);

## Implementations§

source§

### impl<T, const N: usize> HistoryBuffer<T, N>

source

#### pub const fn new() -> Self

Constructs a new history buffer.

The construction of a `HistoryBuffer` works in `const` contexts.

##### Examples

    use heapless::HistoryBuffer;

    // Allocate a 16-element buffer on the stack
    let x: HistoryBuffer<u8, 16> = HistoryBuffer::new();
    assert_eq!(x.len(), 0);

source

#### pub fn clear(&mut self)

Clears the buffer, replacing every element with the default value of type `T`.

source§

### impl<T, const N: usize> HistoryBuffer<T, N>where T: Copy + Clone,

source

#### pub fn new_with(t: T) -> Self

Constructs a new history buffer, where every element is the given value.

##### Examples

    use heapless::HistoryBuffer;

    // Allocate a 16-element buffer on the stack
    let mut x: HistoryBuffer<u8, 16> = HistoryBuffer::new_with(4);
    // All elements are four
    assert_eq!(x.as_slice(), [4; 16]);

source

#### pub fn clear_with(&mut self, t: T)

Clears the buffer, replacing every element with the given value.

source§

### impl<T, const N: usize> HistoryBuffer<T, N>

source

#### pub fn len(&self) -> usize

Returns the current fill level of the buffer.

source

#### pub fn capacity(&self) -> usize

Returns the capacity of the buffer, which is the length of the underlying backing array.

source

#### pub fn write(&mut self, t: T)

Writes an element to the buffer, overwriting the oldest value.

source

#### pub fn extend_from_slice(&mut self, other: &[T])where T: Clone,

Clones and writes all elements in a slice to the buffer.

If the slice is longer than the buffer, only the last `self.len()` elements will actually be stored.

source

#### pub fn recent(&self) -> Option<&T>

Returns a reference to the most recently written value.

##### Examples

    use heapless::HistoryBuffer;

    let mut x: HistoryBuffer<u8, 16> = HistoryBuffer::new();
    x.write(4);
    x.write(10);
    assert_eq!(x.recent(), Some(&10));

source

#### pub fn as_slice(&self) -> &[T]

Returns the array slice backing the buffer, without keeping track of the write position. Therefore, the element order is unspecified.

source

#### pub fn oldest_ordered<'a>(&'a self) -> OldestOrdered<'a, T, N> ⓘ

Returns an iterator for iterating over the buffer from oldest to newest.

##### Examples

    use heapless::HistoryBuffer;

    let mut buffer: HistoryBuffer<u8, 6> = HistoryBuffer::new();
    buffer.extend([0, 0, 0, 1, 2, 3, 4, 5, 6]);
    let expected = [1, 2, 3, 4, 5, 6];
    for (x, y) in buffer.oldest_ordered().zip(expected.iter()) {
        assert_eq!(x, y)
    }

## Methods from Deref<Target = [T]>§

1.23.0

#### pub fn is_ascii(&self) -> bool

Checks if all bytes in this slice are within the ASCII range.

#### pub fn as_ascii(&self) -> Option<&[AsciiChar]>

🔬This is a nightly-only experimental API. (`ascii_char`)

If this slice `is_ascii`, returns it as a slice of ASCII characters, otherwise returns `None`.

#### pub unsafe fn as_ascii_unchecked(&self) -> &[AsciiChar]

🔬This is a nightly-only experimental API. (`ascii_char`)

Converts this slice of bytes into a slice of ASCII characters, without checking whether they’re valid.

##### Safety

Every byte in the slice must be in `0..=127`, or else this is UB.

1.23.0

#### pub fn eq_ignore_ascii_case(&self, other: &[u8]) -> bool

Checks that two slices are an ASCII case-insensitive match.

Same as `to_ascii_lowercase(a) == to_ascii_lowercase(b)`, but without allocating and copying temporaries.

1.60.0

#### pub fn escape_ascii(&self) -> EscapeAscii<'_>

Returns an iterator that produces an escaped version of this slice, treating it as an ASCII string.

##### Examples

    let s = b"0\t\r\n'\"\\\x9d";
    let escaped = s.escape_ascii().to_string();
    assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");

#### pub fn trim_ascii_start(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`byte_slice_trim_ascii`)

Returns a byte slice with leading ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### Examples

    #![feature(byte_slice_trim_ascii)]

    assert_eq!(b" \t hello world\n".trim_ascii_start(), b"hello world\n");
    assert_eq!(b"  ".trim_ascii_start(), b"");
    assert_eq!(b"".trim_ascii_start(), b"");

#### pub fn trim_ascii_end(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`byte_slice_trim_ascii`)

Returns a byte slice with trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### Examples

    #![feature(byte_slice_trim_ascii)]

    assert_eq!(b"\r hello world\n ".trim_ascii_end(), b"\r hello world");
    assert_eq!(b"  ".trim_ascii_end(), b"");
    assert_eq!(b"".trim_ascii_end(), b"");

#### pub fn trim_ascii(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`byte_slice_trim_ascii`)

Returns a byte slice with leading and trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### Examples

    #![feature(byte_slice_trim_ascii)]

    assert_eq!(b"\r hello world\n ".trim_ascii(), b"hello world");
    assert_eq!(b"  ".trim_ascii(), b"");
    assert_eq!(b"".trim_ascii(), b"");

#### pub fn as_str(&self) -> &str

🔬This is a nightly-only experimental API. (`ascii_char`)

Views this slice of ASCII characters as a UTF-8 `str`.

#### pub fn as_bytes(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`ascii_char`)

Views this slice of ASCII characters as a slice of `u8` bytes.

#### pub fn flatten(&self) -> &[T]

🔬This is a nightly-only experimental API. (`slice_flatten`)

Takes a `&[[T; N]]`, and flattens it to a `&[T]`.

##### Panics

This panics if the length of the resulting slice would overflow a `usize`.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If `size_of::<T>() > 0`, this will never panic.

##### Examples

    #![feature(slice_flatten)]

    assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);

    assert_eq!(
        [[1, 2, 3], [4, 5, 6]].flatten(),
        [[1, 2], [3, 4], [5, 6]].flatten(),
    );

    let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
    assert!(slice_of_empty_arrays.flatten().is_empty());

    let empty_slice_of_arrays: &[[u32; 10]] = &[];
    assert!(empty_slice_of_arrays.flatten().is_empty());

1.0.0

#### pub fn len(&self) -> usize

Returns the number of elements in the slice.

##### Examples

    let a = [1, 2, 3];
    assert_eq!(a.len(), 3);

1.0.0

#### pub fn is_empty(&self) -> bool

Returns `true` if the slice has a length of 0.

##### Examples

    let a = [1, 2, 3];
    assert!(!a.is_empty());

1.0.0

#### pub fn first(&self) -> Option<&T>

Returns the first element of the slice, or `None` if it is empty.

##### Examples

    let v = [10, 40, 30];
    assert_eq!(Some(&10), v.first());

    let w: &[i32] = &[];
    assert_eq!(None, w.first());

1.5.0

#### pub fn split_first(&self) -> Option<(&T, &[T])>

Returns the first and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    let x = &[0, 1, 2];

    if let Some((first, elements)) = x.split_first() {
        assert_eq!(first, &0);
        assert_eq!(elements, &[1, 2]);
    }

1.5.0

#### pub fn split_last(&self) -> Option<(&T, &[T])>

Returns the last and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    let x = &[0, 1, 2];

    if let Some((last, elements)) = x.split_last() {
        assert_eq!(last, &2);
        assert_eq!(elements, &[0, 1]);
    }

1.0.0

#### pub fn last(&self) -> Option<&T>

Returns the last element of the slice, or `None` if it is empty.

##### Examples

    let v = [10, 40, 30];
    assert_eq!(Some(&30), v.last());

    let w: &[i32] = &[];
    assert_eq!(None, w.last());

#### pub fn first_chunk<const N: usize>(&self) -> Option<&[T; N]>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk`)

Returns the first `N` elements of the slice, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let u = [10, 40, 30];
    assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());

    let v: &[i32] = &[10];
    assert_eq!(None, v.first_chunk::<2>());

    let w: &[i32] = &[];
    assert_eq!(Some(&[]), w.first_chunk::<0>());

#### pub fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk`)

Returns the first `N` elements of the slice and the remainder, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &[0, 1, 2];

    if let Some((first, elements)) = x.split_first_chunk::<2>() {
        assert_eq!(first, &[0, 1]);
        assert_eq!(elements, &[2]);
    }

#### pub fn split_last_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk`)

Returns the last `N` elements of the slice and the remainder, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &[0, 1, 2];

    if let Some((last, elements)) = x.split_last_chunk::<2>() {
        assert_eq!(last, &[1, 2]);
        assert_eq!(elements, &[0]);
    }

#### pub fn last_chunk<const N: usize>(&self) -> Option<&[T; N]>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk`)

Returns the last element of the slice, or `None` if it is empty.

##### Examples

    #![feature(slice_first_last_chunk)]

    let u = [10, 40, 30];
    assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());

    let v: &[i32] = &[10];
    assert_eq!(None, v.last_chunk::<2>());

    let w: &[i32] = &[];
    assert_eq!(Some(&[]), w.last_chunk::<0>());

1.0.0

#### pub fn get<I>(&self, index: I) -> Option<&<I as SliceIndex<[T]>>::Output>where I: SliceIndex<[T]>,

Returns a reference to an element or subslice depending on the type of index.

- If given a position, returns a reference to the element at that position or `None` if out of bounds.
- If given a range, returns the subslice corresponding to that range, or `None` if out of bounds.

##### Examples

    let v = [10, 40, 30];
    assert_eq!(Some(&40), v.get(1));
    assert_eq!(Some(&[10, 40][..]), v.get(0..2));
    assert_eq!(None, v.get(3));
    assert_eq!(None, v.get(0..4));

1.0.0

#### pub unsafe fn get_unchecked<I>( &self, index: I ) -> &<I as SliceIndex<[T]>>::Outputwhere I: SliceIndex<[T]>,

Returns a reference to an element or subslice, without doing bounds checking.

For a safe alternative see `get`.

##### Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

##### Examples

    let x = &[1, 2, 4];

    unsafe {
        assert_eq!(x.get_unchecked(1), &2);
    }

1.0.0

#### pub fn as_ptr(&self) -> *const T

Returns a raw pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an `UnsafeCell`) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use `as_mut_ptr`.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

##### Examples

    let x = &[1, 2, 4];
    let x_ptr = x.as_ptr();

    unsafe {
        for i in 0..x.len() {
            assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
        }
    }

1.48.0

#### pub fn as_ptr_range(&self) -> Range<*const T>

Returns the two raw pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See `as_ptr` for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

It can also be useful to check if a pointer to an element refers to an element of this slice:

    let a = [1, 2, 3];
    let x = &a[1] as *const _;
    let y = &5 as *const _;

    assert!(a.as_ptr_range().contains(&x));
    assert!(!a.as_ptr_range().contains(&y));

1.0.0

#### pub fn iter(&self) -> Iter<'_, T>

Returns an iterator over the slice.

The iterator yields all items from start to end.

##### Examples

    let x = &[1, 2, 4];
    let mut iterator = x.iter();

    assert_eq!(iterator.next(), Some(&1));
    assert_eq!(iterator.next(), Some(&2));
    assert_eq!(iterator.next(), Some(&4));
    assert_eq!(iterator.next(), None);

1.0.0

#### pub fn windows(&self, size: usize) -> Windows<'_, T>

Returns an iterator over all contiguous windows of length `size`. The windows overlap. If the slice is shorter than `size`, the iterator returns no values.

##### Panics

Panics if `size` is 0.

##### Examples

    let slice = ['r', 'u', 's', 't'];
    let mut iter = slice.windows(2);
    assert_eq!(iter.next().unwrap(), &['r', 'u']);
    assert_eq!(iter.next().unwrap(), &['u', 's']);
    assert_eq!(iter.next().unwrap(), &['s', 't']);
    assert!(iter.next().is_none());

If the slice is shorter than `size`:

    let slice = ['f', 'o', 'o'];
    let mut iter = slice.windows(4);
    assert!(iter.next().is_none());

There’s no `windows_mut`, as that existing would let safe code violate the “only one `&mut` at a time to the same thing” rule. However, you can sometimes use `Cell::as_slice_of_cells` in conjunction with `windows` to accomplish something similar:

    use std::cell::Cell;

    let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
    let slice = &mut array[..];
    let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
    for w in slice_of_cells.windows(3) {
        Cell::swap(&w[0], &w[2]);
    }
    assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);

1.0.0

#### pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T>

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last chunk will not have length `chunk_size`.

See `chunks_exact` for a variant of this iterator that returns chunks of always exactly `chunk_size` elements, and `rchunks` for the same iterator but starting at the end of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.chunks(2);
    assert_eq!(iter.next().unwrap(), &['l', 'o']);
    assert_eq!(iter.next().unwrap(), &['r', 'e']);
    assert_eq!(iter.next().unwrap(), &['m']);
    assert!(iter.next().is_none());

1.31.0

#### pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T>

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved from the `remainder` function of the iterator.

Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the resulting code better than in the case of `chunks`.

See `chunks` for a variant of this iterator that also returns the remainder as a smaller chunk, and `rchunks_exact` for the same iterator but starting at the end of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.chunks_exact(2);
    assert_eq!(iter.next().unwrap(), &['l', 'o']);
    assert_eq!(iter.next().unwrap(), &['r', 'e']);
    assert!(iter.next().is_none());
    assert_eq!(iter.remainder(), &['m']);

#### pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]]

🔬This is a nightly-only experimental API. (`slice_as_chunks`)

Splits the slice into a slice of `N`-element arrays, assuming that there’s no remainder.

##### Safety

This may only be called when

- The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
- `N != 0`.

##### Examples

    #![feature(slice_as_chunks)]
    let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
    let chunks: &[[char; 1]] =
        // SAFETY: 1-element chunks never have remainder
        unsafe { slice.as_chunks_unchecked() };
    assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
    let chunks: &[[char; 3]] =
        // SAFETY: The slice length (6) is a multiple of 3
        unsafe { slice.as_chunks_unchecked() };
    assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);

    // These would be unsound:
    // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
    // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed

#### pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T])

🔬This is a nightly-only experimental API. (`slice_as_chunks`)

Splits the slice into a slice of `N`-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than `N`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(slice_as_chunks)]
    let slice = ['l', 'o', 'r', 'e', 'm'];
    let (chunks, remainder) = slice.as_chunks();
    assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
    assert_eq!(remainder, &['m']);

If you expect the slice to be an exact multiple, you can combine `let`-`else` with an empty slice pattern:

    #![feature(slice_as_chunks)]
    let slice = ['R', 'u', 's', 't'];
    let (chunks, []) = slice.as_chunks::<2>() else {
        panic!("slice didn't have even length")
    };
    assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);

#### pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]])

🔬This is a nightly-only experimental API. (`slice_as_chunks`)

Splits the slice into a slice of `N`-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than `N`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(slice_as_chunks)]
    let slice = ['l', 'o', 'r', 'e', 'm'];
    let (remainder, chunks) = slice.as_rchunks();
    assert_eq!(remainder, &['l']);
    assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);

#### pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N>

🔬This is a nightly-only experimental API. (`array_chunks`)

Returns an iterator over `N` elements of the slice at a time, starting at the beginning of the slice.

The chunks are array references and do not overlap. If `N` does not divide the length of the slice, then the last up to `N-1` elements will be omitted and can be retrieved from the `remainder` function of the iterator.

This method is the const generic equivalent of `chunks_exact`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(array_chunks)]
    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.array_chunks();
    assert_eq!(iter.next().unwrap(), &['l', 'o']);
    assert_eq!(iter.next().unwrap(), &['r', 'e']);
    assert!(iter.next().is_none());
    assert_eq!(iter.remainder(), &['m']);

#### pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N>

🔬This is a nightly-only experimental API. (`array_windows`)

Returns an iterator over overlapping windows of `N` elements of a slice, starting at the beginning of the slice.

This is the const generic equivalent of `windows`.

If `N` is greater than the size of the slice, it will return no windows.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(array_windows)]
    let slice = [0, 1, 2, 3];
    let mut iter = slice.array_windows();
    assert_eq!(iter.next().unwrap(), &[0, 1]);
    assert_eq!(iter.next().unwrap(), &[1, 2]);
    assert_eq!(iter.next().unwrap(), &[2, 3]);
    assert!(iter.next().is_none());

1.31.0

#### pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T>

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last chunk will not have length `chunk_size`.

See `rchunks_exact` for a variant of this iterator that returns chunks of always exactly `chunk_size` elements, and `chunks` for the same iterator but starting at the beginning of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.rchunks(2);
    assert_eq!(iter.next().unwrap(), &['e', 'm']);
    assert_eq!(iter.next().unwrap(), &['o', 'r']);
    assert_eq!(iter.next().unwrap(), &['l']);
    assert!(iter.next().is_none());

1.31.0

#### pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T>

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved from the `remainder` function of the iterator.

Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the resulting code better than in the case of `rchunks`.

See `rchunks` for a variant of this iterator that also returns the remainder as a smaller chunk, and `chunks_exact` for the same iterator but starting at the beginning of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.rchunks_exact(2);
    assert_eq!(iter.next().unwrap(), &['e', 'm']);
    assert_eq!(iter.next().unwrap(), &['o', 'r']);
    assert!(iter.next().is_none());
    assert_eq!(iter.remainder(), &['l']);

#### pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>where F: FnMut(&T, &T) -> bool,

🔬This is a nightly-only experimental API. (`slice_group_by`)

Returns an iterator over the slice producing non-overlapping runs of elements using the predicate to separate them.

The predicate is called on two elements following themselves, it means the predicate is called on `slice[0]` and `slice[1]` then on `slice[1]` and `slice[2]` and so on.

##### Examples

    #![feature(slice_group_by)]

    let slice = &[1, 1, 1, 3, 3, 2, 2, 2];

    let mut iter = slice.group_by(|a, b| a == b);

    assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
    assert_eq!(iter.next(), Some(&[3, 3][..]));
    assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
    assert_eq!(iter.next(), None);

This method can be used to extract the sorted subslices:

    #![feature(slice_group_by)]

    let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];

    let mut iter = slice.group_by(|a, b| a <= b);

    assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
    assert_eq!(iter.next(), Some(&[2, 3][..]));
    assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
    assert_eq!(iter.next(), None);

1.0.0

#### pub fn split_at(&self, mid: usize) -> (&[T], &[T])

Divides one slice into two at an index.

The first will contain all indices from `[0, mid)` (excluding the index `mid` itself) and the second will contain all indices from `[mid, len)` (excluding the index `len` itself).

##### Panics

Panics if `mid > len`.

##### Examples

    let v = [1, 2, 3, 4, 5, 6];

    {
       let (left, right) = v.split_at(0);
       assert_eq!(left, []);
       assert_eq!(right, [1, 2, 3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_at(2);
        assert_eq!(left, [1, 2]);
        assert_eq!(right, [3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_at(6);
        assert_eq!(left, [1, 2, 3, 4, 5, 6]);
        assert_eq!(right, []);
    }

#### pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T])

🔬This is a nightly-only experimental API. (`slice_split_at_unchecked`)

Divides one slice into two at an index, without doing bounds checking.

The first will contain all indices from `[0, mid)` (excluding the index `mid` itself) and the second will contain all indices from `[mid, len)` (excluding the index `len` itself).

For a safe alternative see `split_at`.

##### Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that `0 <= mid <= self.len()`.

##### Examples

    #![feature(slice_split_at_unchecked)]

    let v = [1, 2, 3, 4, 5, 6];

    unsafe {
       let (left, right) = v.split_at_unchecked(0);
       assert_eq!(left, []);
       assert_eq!(right, [1, 2, 3, 4, 5, 6]);
    }

    unsafe {
        let (left, right) = v.split_at_unchecked(2);
        assert_eq!(left, [1, 2]);
        assert_eq!(right, [3, 4, 5, 6]);
    }

    unsafe {
        let (left, right) = v.split_at_unchecked(6);
        assert_eq!(left, [1, 2, 3, 4, 5, 6]);
        assert_eq!(right, []);
    }

#### pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T])

🔬This is a nightly-only experimental API. (`split_array`)

Divides one slice into an array and a remainder slice at an index.

The array will contain all indices from `[0, N)` (excluding the index `N` itself) and the slice will contain all indices from `[N, len)` (excluding the index `len` itself).

##### Panics

Panics if `N > len`.

##### Examples

    #![feature(split_array)]

    let v = &[1, 2, 3, 4, 5, 6][..];

    {
       let (left, right) = v.split_array_ref::<0>();
       assert_eq!(left, &[]);
       assert_eq!(right, [1, 2, 3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_array_ref::<2>();
        assert_eq!(left, &[1, 2]);
        assert_eq!(right, [3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_array_ref::<6>();
        assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
        assert_eq!(right, []);
    }

#### pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N])

🔬This is a nightly-only experimental API. (`split_array`)

Divides one slice into an array and a remainder slice at an index from the end.

The slice will contain all indices from `[0, len - N)` (excluding the index `len - N` itself) and the array will contain all indices from `[len - N, len)` (excluding the index `len` itself).

##### Panics

Panics if `N > len`.

##### Examples

    #![feature(split_array)]

    let v = &[1, 2, 3, 4, 5, 6][..];

    {
       let (left, right) = v.rsplit_array_ref::<0>();
       assert_eq!(left, [1, 2, 3, 4, 5, 6]);
       assert_eq!(right, &[]);
    }

    {
        let (left, right) = v.rsplit_array_ref::<2>();
        assert_eq!(left, [1, 2, 3, 4]);
        assert_eq!(right, &[5, 6]);
    }

    {
        let (left, right) = v.rsplit_array_ref::<6>();
        assert_eq!(left, []);
        assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
    }

1.0.0

#### pub fn split<F>(&self, pred: F) -> Split<'_, T, F>where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`. The matched element is not contained in the subslices.

##### Examples

    let slice = [10, 40, 33, 20];
    let mut iter = slice.split(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10, 40]);
    assert_eq!(iter.next().unwrap(), &[20]);
    assert!(iter.next().is_none());

If the first element is matched, an empty slice will be the first item returned by the iterator. Similarly, if the last element in the slice is matched, an empty slice will be the last item returned by the iterator:

    let slice = [10, 40, 33];
    let mut iter = slice.split(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10, 40]);
    assert_eq!(iter.next().unwrap(), &[]);
    assert!(iter.next().is_none());

If two matched elements are directly adjacent, an empty slice will be present between them:

    let slice = [10, 6, 33, 20];
    let mut iter = slice.split(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10]);
    assert_eq!(iter.next().unwrap(), &[]);
    assert_eq!(iter.next().unwrap(), &[20]);
    assert!(iter.next().is_none());

1.51.0

#### pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`. The matched element is contained in the end of the previous subslice as a terminator.

##### Examples

    let slice = [10, 40, 33, 20];
    let mut iter = slice.split_inclusive(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
    assert_eq!(iter.next().unwrap(), &[20]);
    assert!(iter.next().is_none());

If the last element of the slice is matched, that element will be considered the terminator of the preceding slice. That slice will be the last item returned by the iterator.

    let slice = [3, 10, 40, 33];
    let mut iter = slice.split_inclusive(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[3]);
    assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
    assert!(iter.next().is_none());

1.27.0

#### pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

##### Examples

    let slice = [11, 22, 33, 0, 44, 55];
    let mut iter = slice.rsplit(|num| *num == 0);

    assert_eq!(iter.next().unwrap(), &[44, 55]);
    assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
    assert_eq!(iter.next(), None);

As with `split()`, if the first or last element is matched, an empty slice will be the first (or last) item returned by the iterator.

    let v = &[0, 1, 1, 2, 3, 5, 8];
    let mut it = v.rsplit(|n| *n % 2 == 0);
    assert_eq!(it.next().unwrap(), &[]);
    assert_eq!(it.next().unwrap(), &[3, 5]);
    assert_eq!(it.next().unwrap(), &[1, 1]);
    assert_eq!(it.next().unwrap(), &[]);
    assert_eq!(it.next(), None);

1.0.0

#### pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`, limited to returning at most `n` items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

##### Examples

Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`, `[20, 60, 50]`):

    let v = [10, 40, 30, 20, 60, 50];

    for group in v.splitn(2, |num| *num % 3 == 0) {
        println!("{group:?}");
    }

1.0.0

#### pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>where F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred` limited to returning at most `n` items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

##### Examples

Print the slice split once, starting from the end, by numbers divisible by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):

    let v = [10, 40, 30, 20, 60, 50];

    for group in v.rsplitn(2, |num| *num % 3 == 0) {
        println!("{group:?}");
    }

1.0.0

#### pub fn contains(&self, x: &T) -> boolwhere T: PartialEq<T>,

Returns `true` if the slice contains an element with the given value.

This operation is O(n).

Note that if you have a sorted slice, `binary_search` may be faster.

##### Examples

    let v = [10, 40, 30];
    assert!(v.contains(&30));
    assert!(!v.contains(&50));

If you do not have a `&T`, but some other value that you can compare with one (for example, `String` implements `PartialEq<str>`), you can use `iter().any`:

    let v = [String::from("hello"), String::from("world")]; // slice of `String`
    assert!(v.iter().any(|e| e == "hello")); // search with `&str`
    assert!(!v.iter().any(|e| e == "hi"));

1.0.0

#### pub fn starts_with(&self, needle: &[T]) -> boolwhere T: PartialEq<T>,

Returns `true` if `needle` is a prefix of the slice.

##### Examples

    let v = [10, 40, 30];
    assert!(v.starts_with(&[10]));
    assert!(v.starts_with(&[10, 40]));
    assert!(!v.starts_with(&[50]));
    assert!(!v.starts_with(&[10, 50]));

Always returns `true` if `needle` is an empty slice:

    let v = &[10, 40, 30];
    assert!(v.starts_with(&[]));
    let v: &[u8] = &[];
    assert!(v.starts_with(&[]));

1.0.0

#### pub fn ends_with(&self, needle: &[T]) -> boolwhere T: PartialEq<T>,

Returns `true` if `needle` is a suffix of the slice.

##### Examples

    let v = [10, 40, 30];
    assert!(v.ends_with(&[30]));
    assert!(v.ends_with(&[40, 30]));
    assert!(!v.ends_with(&[50]));
    assert!(!v.ends_with(&[50, 30]));

Always returns `true` if `needle` is an empty slice:

    let v = &[10, 40, 30];
    assert!(v.ends_with(&[]));
    let v: &[u8] = &[];
    assert!(v.ends_with(&[]));

1.51.0

#### pub fn strip_prefix<P>(&self, prefix: &P) -> Option<&[T]>where P: SlicePattern<Item = T> + ?Sized, T: PartialEq<T>,

Returns a subslice with the prefix removed.

If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`. If `prefix` is empty, simply returns the original slice.

If the slice does not start with `prefix`, returns `None`.

##### Examples

    let v = &[10, 40, 30];
    assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
    assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
    assert_eq!(v.strip_prefix(&[50]), None);
    assert_eq!(v.strip_prefix(&[10, 50]), None);

    let prefix : &str = "he";
    assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
               Some(b"llo".as_ref()));

1.51.0

#### pub fn strip_suffix<P>(&self, suffix: &P) -> Option<&[T]>where P: SlicePattern<Item = T> + ?Sized, T: PartialEq<T>,

Returns a subslice with the suffix removed.

If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`. If `suffix` is empty, simply returns the original slice.

If the slice does not end with `suffix`, returns `None`.

##### Examples

    let v = &[10, 40, 30];
    assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
    assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
    assert_eq!(v.strip_suffix(&[50]), None);
    assert_eq!(v.strip_suffix(&[50, 30]), None);

1.0.0

#### pub fn binary_search(&self, x: &T) -> Result<usize, usize>where T: Ord,

Binary searches this slice for a given element. If the slice is not sorted, the returned result is unspecified and meaningless.

If the value is found then [`Result::Ok`] is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then [`Result::Err`] is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also `binary_search_by`, `binary_search_by_key`, and `partition_point`.

##### Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in `[1, 4]`.

    let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

    assert_eq!(s.binary_search(&13),  Ok(9));
    assert_eq!(s.binary_search(&4),   Err(7));
    assert_eq!(s.binary_search(&100), Err(13));
    let r = s.binary_search(&1);
    assert!(match r { Ok(1..=4) => true, _ => false, });

If you want to find that whole range of matching items, rather than an arbitrary matching one, that can be done using `partition_point`:

    let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

    let low = s.partition_point(|x| x < &1);
    assert_eq!(low, 1);
    let high = s.partition_point(|x| x <= &1);
    assert_eq!(high, 5);
    let r = s.binary_search(&1);
    assert!((low..high).contains(&r.unwrap()));

    assert!(s[..low].iter().all(|&x| x < 1));
    assert!(s[low..high].iter().all(|&x| x == 1));
    assert!(s[high..].iter().all(|&x| x > 1));

    // For something not found, the "range" of equal items is empty
    assert_eq!(s.partition_point(|x| x < &11), 9);
    assert_eq!(s.partition_point(|x| x <= &11), 9);
    assert_eq!(s.binary_search(&11), Err(9));

If you want to insert an item to a sorted vector, while maintaining sort order, consider using `partition_point`:

    let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
    let num = 42;
    let idx = s.partition_point(|&x| x < num);
    // The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);`
    s.insert(idx, num);
    assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

1.0.0

#### pub fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>where F: FnMut(&'a T) -> Ordering,

Binary searches this slice with a comparator function.

The comparator function should return an order code that indicates whether its argument is `Less`, `Equal` or `Greater` the desired target. If the slice is not sorted or if the comparator function does not implement an order consistent with the sort order of the underlying slice, the returned result is unspecified and meaningless.

If the value is found then [`Result::Ok`] is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then [`Result::Err`] is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also `binary_search`, `binary_search_by_key`, and `partition_point`.

##### Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in `[1, 4]`.

    let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

    let seek = 13;
    assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
    let seek = 4;
    assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
    let seek = 100;
    assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
    let seek = 1;
    let r = s.binary_search_by(|probe| probe.cmp(&seek));
    assert!(match r { Ok(1..=4) => true, _ => false, });

1.10.0

#### pub fn binary_search_by_key<'a, B, F>( &'a self, b: &B, f: F ) -> Result<usize, usize>where F: FnMut(&'a T) -> B, B: Ord,

Binary searches this slice with a key extraction function.

Assumes that the slice is sorted by the key, for instance with `sort_by_key` using the same key extraction function. If the slice is not sorted by the key, the returned result is unspecified and meaningless.

If the value is found then [`Result::Ok`] is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then [`Result::Err`] is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also `binary_search`, `binary_search_by`, and `partition_point`.

##### Examples

Looks up a series of four elements in a slice of pairs sorted by their second elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in `[1, 4]`.

    let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
             (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
             (1, 21), (2, 34), (4, 55)];

    assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b),  Ok(9));
    assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b),   Err(7));
    assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
    let r = s.binary_search_by_key(&1, |&(a, b)| b);
    assert!(match r { Ok(1..=4) => true, _ => false, });

1.30.0

#### pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T])

Transmute the slice to a slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. How exactly the slice is split up is not specified; the middle part may be smaller than necessary. However, if this fails to return a maximal middle part, that is because code is running in a context where performance does not matter, such as a sanitizer attempting to find alignment bugs. Regular code running in a default (debug or release) execution will return a maximal middle part.

This method has no purpose when either input element `T` or output element `U` are zero-sized and will return the original slice without splitting anything.

##### Safety

This method is essentially a `transmute` with respect to the elements in the returned middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.

##### Examples

Basic usage:

    unsafe {
        let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
        let (prefix, shorts, suffix) = bytes.align_to::<u16>();
        // less_efficient_algorithm_for_bytes(prefix);
        // more_efficient_algorithm_for_aligned_shorts(shorts);
        // less_efficient_algorithm_for_bytes(suffix);
    }

#### pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])where Simd<T, LANES>: AsRef<[T; LANES]>, T: SimdElement, LaneCount<LANES>: SupportedLaneCount,

🔬This is a nightly-only experimental API. (`portable_simd`)

Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.

This is a safe wrapper around [`slice::align_to`], so has the same weak postconditions as that method. You’re only assured that `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.

Notably, all of the following are possible:

- `prefix.len() >= LANES`.
- `middle.is_empty()` despite `self.len() >= 3 * LANES`.
- `suffix.len() >= LANES`.

That said, this is a safe method, so if you’re only writing safe code, then this can at most cause incorrect logic, not unsoundness.

##### Panics

This will panic if the size of the SIMD type is different from `LANES` times that of the scalar.

At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like `LANES == 3`.

##### Examples

    #![feature(portable_simd)]
    use core::simd::SimdFloat;

    let short = &[1, 2, 3];
    let (prefix, middle, suffix) = short.as_simd::<4>();
    assert_eq!(middle, []); // Not enough elements for anything in the middle

    // They might be split in any possible way between prefix and suffix
    let it = prefix.iter().chain(suffix).copied();
    assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);

    fn basic_simd_sum(x: &[f32]) -> f32 {
        use std::ops::Add;
        use std::simd::f32x4;
        let (prefix, middle, suffix) = x.as_simd();
        let sums = f32x4::from_array([
            prefix.iter().copied().sum(),
            0.0,
            0.0,
            suffix.iter().copied().sum(),
        ]);
        let sums = middle.iter().copied().fold(sums, f32x4::add);
        sums.reduce_sum()
    }

    let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
    assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);

#### pub fn is_sorted(&self) -> boolwhere T: PartialOrd<T>,

🔬This is a nightly-only experimental API. (`is_sorted`)

Checks if the elements of this slice are sorted.

That is, for each element `a` and its following element `b`, `a <= b` must hold. If the slice yields exactly zero or one element, `true` is returned.

Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition implies that this function returns `false` if any two consecutive items are not comparable.

##### Examples

    #![feature(is_sorted)]
    let empty: [i32; 0] = [];

    assert!([1, 2, 2, 9].is_sorted());
    assert!(![1, 3, 2, 4].is_sorted());
    assert!([0].is_sorted());
    assert!(empty.is_sorted());
    assert!(![0.0, 1.0, f32::NAN].is_sorted());

#### pub fn is_sorted_by<'a, F>(&'a self, compare: F) -> boolwhere F: FnMut(&'a T, &'a T) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (`is_sorted`)

Checks if the elements of this slice are sorted using the given comparator function.

Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` function to determine the ordering of two elements. Apart from that, it’s equivalent to `is_sorted`; see its documentation for more information.

#### pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> boolwhere F: FnMut(&'a T) -> K, K: PartialOrd<K>,

🔬This is a nightly-only experimental API. (`is_sorted`)

Checks if the elements of this slice are sorted using the given key extraction function.

Instead of comparing the slice’s elements directly, this function compares the keys of the elements, as determined by `f`. Apart from that, it’s equivalent to `is_sorted`; see its documentation for more information.

##### Examples

    #![feature(is_sorted)]

    assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
    assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));

1.52.0

#### pub fn partition_point<P>(&self, pred: P) -> usizewhere P: FnMut(&T) -> bool,

Returns the index of the partition point according to the given predicate (the index of the first element of the second partition).

The slice is assumed to be partitioned according to the given predicate. This means that all elements for which the predicate returns true are at the start of the slice and all elements for which the predicate returns false are at the end. For example, `[7, 15, 3, 5, 4, 12, 6]` is partitioned under the predicate `x % 2 != 0` (all odd numbers are at the start, all even at the end).

If this slice is not partitioned, the returned result is unspecified and meaningless, as this method performs a kind of binary search.

See also `binary_search`, `binary_search_by`, and `binary_search_by_key`.

##### Examples

    let v = [1, 2, 3, 3, 5, 6, 7];
    let i = v.partition_point(|&x| x < 5);

    assert_eq!(i, 4);
    assert!(v[..i].iter().all(|&x| x < 5));
    assert!(v[i..].iter().all(|&x| !(x < 5)));

If all elements of the slice match the predicate, including if the slice is empty, then the length of the slice will be returned:

    let a = [2, 4, 8];
    assert_eq!(a.partition_point(|x| x < &100), a.len());
    let a: [i32; 0] = [];
    assert_eq!(a.partition_point(|x| x < &100), 0);

If you want to insert an item to a sorted vector, while maintaining sort order:

    let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
    let num = 42;
    let idx = s.partition_point(|&x| x < num);
    s.insert(idx, num);
    assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

## Trait Implementations§

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### impl<T, const N: usize> AsRef<[T]> for HistoryBuffer<T, N>

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#### fn as_ref(&self) -> &[T]

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#### fn drop(&mut self)

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### impl<'a, T, const N: usize> Extend<&'a T> for HistoryBuffer<T, N>where T: 'a + Clone,

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#### fn extend<I>(&mut self, iter: I)where I: IntoIterator<Item = &'a T>,

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one`)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

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### impl<T, const N: usize> Extend<T> for HistoryBuffer<T, N>

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#### fn extend<I>(&mut self, iter: I)where I: IntoIterator<Item = T>,

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one`)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one`)
Reserves capacity in a collection for the given number of additional elements. Read more

## Auto Trait Implementations§

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### impl<T, const N: usize> RefUnwindSafe for HistoryBuffer<T, N>where T: RefUnwindSafe,

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### impl<T, const N: usize> Send for HistoryBuffer<T, N>where T: Send,

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### impl<T, const N: usize> Sync for HistoryBuffer<T, N>where T: Sync,

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### impl<T, const N: usize> Unpin for HistoryBuffer<T, N>where T: Unpin,

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### impl<T, const N: usize> UnwindSafe for HistoryBuffer<T, N>where T: UnwindSafe,

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