smallvec 2.0.0-beta.5

'Small vector' optimization: store up to a small number of items on the stack
Documentation 
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use {
    super::SmallVec,
    core::{
        alloc::Allocator,
        borrow::{
            Borrow,
            BorrowMut
        },
        ops::{
            Deref,
            DerefMut
        },
        slice::{
            from_raw_parts,
            from_raw_parts_mut
        }
    }
};

impl<Item, const INLINE: usize, Heap: Allocator> Borrow<[Item]> for SmallVec<Item, INLINE, Heap> {
    #[inline]
    fn borrow(&self) -> &[Item] { self.as_ref() }
}

impl<Item, const INLINE: usize, Heap: Allocator> BorrowMut<[Item]>
    for SmallVec<Item, INLINE, Heap>
{
    #[inline]
    fn borrow_mut(&mut self) -> &mut [Item] { self.as_mut() }
}

impl<Item, const INLINE: usize, Heap: Allocator> AsRef<[Item]> for SmallVec<Item, INLINE, Heap> {
    #[inline]
    fn as_ref(&self) -> &[Item] {
        let (length, spilled) = self.length.parts();
        // SAFETY: all the elements in `..length` are initialized
        unsafe { from_raw_parts(self.raw.as_ptr(spilled), length) }
    }
}

impl<Item, const INLINE: usize, Heap: Allocator> AsMut<[Item]> for SmallVec<Item, INLINE, Heap> {
    #[inline]
    fn as_mut(&mut self) -> &mut [Item] {
        let (length, spilled) = self.length.parts();
        // SAFETY: see above
        unsafe { from_raw_parts_mut(self.raw.as_mut_ptr(spilled), length) }
    }
}

impl<Item, const INLINE: usize, Heap: Allocator> Deref for SmallVec<Item, INLINE, Heap> {
    type Target = [Item];

    #[inline]
    fn deref(&self) -> &Self::Target { self.as_ref() }
}

impl<Item, const INLINE: usize, Heap: Allocator> DerefMut for SmallVec<Item, INLINE, Heap> {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target { self.as_mut() }
}

#[cfg(feature = "deref-pure")]
unsafe impl<Item, const INLINE: usize, Heap: Allocator> core::ops::DerefPure
    for SmallVec<Item, INLINE, Heap>
{
}