rune/shared/
fixed_vec.rs

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1use core::mem::{self, ManuallyDrop, MaybeUninit};
2use core::ops::{Deref, DerefMut};
3use core::ptr;
4use core::slice;
5
6use crate::alloc;
7
8/// A fixed capacity vector allocated on the stack.
9pub(crate) struct FixedVec<T, const N: usize> {
10    data: [MaybeUninit<T>; N],
11    len: usize,
12}
13
14impl<T, const N: usize> FixedVec<T, N> {
15    /// Construct a new empty fixed vector.
16    pub(crate) const fn new() -> FixedVec<T, N> {
17        unsafe {
18            FixedVec {
19                data: MaybeUninit::uninit().assume_init(),
20                len: 0,
21            }
22        }
23    }
24
25    #[inline]
26    pub(crate) fn as_ptr(&self) -> *const T {
27        self.data.as_ptr() as *const T
28    }
29
30    #[inline]
31    pub(crate) fn as_mut_ptr(&mut self) -> *mut T {
32        self.data.as_mut_ptr() as *mut T
33    }
34
35    #[inline]
36    pub(crate) fn as_slice(&self) -> &[T] {
37        unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
38    }
39
40    #[inline]
41    pub(crate) fn as_mut_slice(&mut self) -> &mut [T] {
42        unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
43    }
44
45    /// Try to push an element onto the fixed vector.
46    pub(crate) fn try_push(&mut self, element: T) -> alloc::Result<()> {
47        if self.len >= N {
48            return Err(alloc::Error::CapacityOverflow);
49        }
50
51        unsafe {
52            ptr::write(self.as_mut_ptr().wrapping_add(self.len), element);
53            self.len += 1;
54        }
55
56        Ok(())
57    }
58
59    pub(crate) fn clear(&mut self) {
60        if self.len == 0 {
61            return;
62        }
63
64        let len = mem::take(&mut self.len);
65
66        if mem::needs_drop::<T>() {
67            unsafe {
68                let tail = slice::from_raw_parts_mut(self.as_mut_ptr(), len);
69                ptr::drop_in_place(tail);
70            }
71        }
72    }
73
74    /// Coerce into an array if the size of the array matches what's expected or panic.
75    pub(crate) fn into_inner(self) -> [T; N] {
76        let len = self.len;
77
78        let Some(array) = self.try_into_inner() else {
79            panic!("into_inner: length mismatch, expected {N} but got {len}");
80        };
81
82        array
83    }
84
85    /// Coerce into an array if the size of the array matches what's expected.
86    pub(crate) fn try_into_inner(self) -> Option<[T; N]> {
87        if self.len != N {
88            return None;
89        }
90
91        // SAFETY: We've asserted that the length is initialized just above.
92        unsafe {
93            let this = ManuallyDrop::new(self);
94            Some(ptr::read(this.data.as_ptr() as *const [T; N]))
95        }
96    }
97}
98
99impl<T, const N: usize> Deref for FixedVec<T, N> {
100    type Target = [T];
101
102    #[inline]
103    fn deref(&self) -> &Self::Target {
104        self.as_slice()
105    }
106}
107
108impl<T, const N: usize> DerefMut for FixedVec<T, N> {
109    #[inline]
110    fn deref_mut(&mut self) -> &mut Self::Target {
111        self.as_mut_slice()
112    }
113}
114
115impl<T, const N: usize> Drop for FixedVec<T, N> {
116    #[inline]
117    fn drop(&mut self) {
118        self.clear()
119    }
120}
rune/shared/fixed_vec.rs

rune/shared/
fixed_vec.rs
