array_concat/
lib.rs

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1#![no_std]
2
3/// Computes total size of all provided const arrays.
4#[macro_export]
5macro_rules! concat_arrays_size {
6    ($( $array:expr ),*) => {{
7        0 $(+ $array.len())*
8    }};
9}
10
11/// Concatenates provided arrays.
12#[macro_export]
13macro_rules! concat_arrays {
14    ($( $array:expr ),*) => ({
15        #[repr(C)]
16        struct ArrayConcatDecomposed<T, A, B>(core::mem::ManuallyDrop<[T; 0]>, core::mem::ManuallyDrop<A>, core::mem::ManuallyDrop<B>);
17
18        impl<T> ArrayConcatDecomposed<T, [T; 0], [T; 0]> {
19            #[inline(always)]
20            const fn default() -> Self {
21                Self::new(core::mem::ManuallyDrop::new([]), [])
22            }
23        }
24        impl<T, A, B> ArrayConcatDecomposed<T, A, B> {
25            #[inline(always)]
26            const fn new(a: core::mem::ManuallyDrop<A>, b: B) -> Self {
27                Self(core::mem::ManuallyDrop::new([]), a, core::mem::ManuallyDrop::new(b))
28            }
29            #[inline(always)]
30            const fn concat<const N: usize>(self, v: [T; N]) -> ArrayConcatDecomposed<T, A, ArrayConcatDecomposed<T, B, [T; N]>> {
31                ArrayConcatDecomposed::new(self.1, ArrayConcatDecomposed::new(self.2, v))
32            }
33        }
34
35        #[repr(C)]
36        union ArrayConcatComposed<T, A, B, const N: usize> {
37            full: core::mem::ManuallyDrop<[T; N]>,
38            decomposed: core::mem::ManuallyDrop<ArrayConcatDecomposed<T, A, B>>,
39        }
40
41        impl<T, A, B, const N: usize> ArrayConcatComposed<T, A, B, N> {
42            const PANIC: bool = $crate::_const_assert_same_size::<[T; N], Self>();
43
44            #[inline(always)]
45            const fn have_same_size(&self) -> bool {
46                Self::PANIC
47            }
48        }
49
50        let composed = ArrayConcatComposed {
51            decomposed: core::mem::ManuallyDrop::new(
52                ArrayConcatDecomposed::default()$(.concat($array))*,
53            )
54        };
55
56        // Sanity check that composed's two fields are the same size
57        composed.have_same_size();
58
59        // SAFETY: Sizes of both fields in composed are the same so this assignment should be sound
60        core::mem::ManuallyDrop::into_inner(unsafe { composed.full })
61    });
62}
63
64/// Flatten a nested tuple based on the number of nestings.
65///
66/// This is an implementation detail of the crate and should only be used by the
67/// macros in this crate.
68#[macro_export]
69#[doc(hidden)]
70macro_rules! flatten_split {
71    (($($tail:tt)*), $head:expr, $pop:expr) => {
72        ($head, $($tail)*)
73    };
74    // We can dramatically reduce macro recursion by adding an additional_case
75    (($($tail:tt)*), $head:expr, $pop1:expr, $pop2:expr$(, $remaining:expr)+) => {
76        $crate::flatten_split!(
77            ($head.1.2, $head.2, $($tail)*),
78            $head.1.1$(,
79            $remaining)+
80        )
81    };
82    (($($tail:tt)*), $head:expr, $pop:expr$(, $remaining:expr)+) => {
83        $crate::flatten_split!(
84            ($head.2, $($tail)*),
85            $head.1$(,
86            $remaining)+
87        )
88    };
89}
90
91/// Split the provided array into the specified sizes.
92#[macro_export]
93macro_rules! split_array {
94    ($array:expr, $size:expr) => ($array);
95    ($array:expr, $size0:expr, $($sizes:expr),+) => ({
96        struct ArrayConcatDecomposedMarkerBase<T, A>(core::marker::PhantomData<(T, A)>);
97        struct ArrayConcatDecomposedMarker<T, A, B>(core::marker::PhantomData<(T, A, B)>);
98
99        #[repr(C)]
100        struct ArrayConcatDecomposed<T, A, B>([T; 0], A, B);
101
102        trait Storage {
103            type Data;
104        }
105        impl<T, const A: usize> Storage for [T; A] {
106            type Data = [T; A];
107        }
108
109        impl<T> ArrayConcatDecomposedMarkerBase<T, ()> {
110            #[inline(always)]
111            const fn default(_: &[T]) -> Self {
112                Self(core::marker::PhantomData)
113            }
114            #[inline(always)]
115            const fn concat<const N: usize>(self, _: [(); N]) -> ArrayConcatDecomposedMarkerBase<T, [T; N]> {
116                ArrayConcatDecomposedMarkerBase(core::marker::PhantomData)
117            }
118        }
119        impl<T, const A: usize> ArrayConcatDecomposedMarkerBase<T, [T; A]> {
120            #[inline(always)]
121            const fn concat<const B: usize>(self, _: [(); B]) -> ArrayConcatDecomposedMarker<T, [T; A], [T; B]> {
122                ArrayConcatDecomposedMarker(core::marker::PhantomData)
123            }
124        }
125
126        impl<T, A: Storage, B: Storage> Storage for ArrayConcatDecomposedMarker<T, A, B> {
127            type Data = ArrayConcatDecomposed<T, A::Data, B::Data>;
128        }
129
130        impl<T, A: Storage, B: Storage> ArrayConcatDecomposedMarker<T, A, B> {
131            #[inline(always)]
132            const fn concat<const C: usize>(self, _: [(); C]) -> ArrayConcatDecomposedMarker<T, ArrayConcatDecomposedMarker<T, A, B>, [T; C]> {
133                ArrayConcatDecomposedMarker(core::marker::PhantomData)
134            }
135            #[inline(always)]
136            const fn make<const N: usize>(self, full: [T; N]) -> ArrayConcatDecomposed<T, A::Data, B::Data> {
137                #[repr(C)]
138                union ArrayConcatComposed<T, A, B, const N: usize> {
139                    full: core::mem::ManuallyDrop<[T; N]>,
140                    decomposed: core::mem::ManuallyDrop<ArrayConcatDecomposed<T, A, B>>,
141                }
142
143                impl<T, A, B, const N: usize> ArrayConcatComposed<T, A, B, N> {
144                    const PANIC: bool = $crate::_const_assert_same_size::<[T; N], Self>();
145
146                    #[inline(always)]
147                    const fn have_same_size(&self) -> bool {
148                        Self::PANIC
149                    }
150                }
151
152                let composed = ArrayConcatComposed::<T, A::Data, B::Data, N> {
153                    full: core::mem::ManuallyDrop::new(full)
154                };
155
156                // Sanity check that composed's two fields are the same size
157                composed.have_same_size();
158
159                // SAFETY: Sizes of both fields in composed are the same so this assignment should be sound
160                core::mem::ManuallyDrop::into_inner(unsafe { composed.decomposed })
161            }
162        }
163
164
165        let array = $array;
166        let decomposed = ArrayConcatDecomposedMarkerBase::default(&array)
167            .concat([(); $size0])
168            $(.concat([(); $sizes]))
169            *.make(array);
170
171        $crate::flatten_split!((), decomposed, $size0$(, $sizes)*)
172    });
173}
174
175/// Assert at compile time that these types have the same size.
176///
177/// This is an implementation detail of the crate and should only be used by the
178/// macros in this crate.
179#[inline(always)]
180#[doc(hidden)]
181pub const fn _const_assert_same_size<A, B>() -> bool {
182    let have_same_size = core::mem::size_of::<A>() == core::mem::size_of::<B>();
183
184    #[cfg(feature = "const_panic")]
185    {
186        have_same_size || panic!("Size Mismatch")
187    }
188
189    #[cfg(not(feature = "const_panic"))]
190    {
191        !["Size mismatch"][!have_same_size as usize].is_empty()
192    }
193}
194
195#[allow(dead_code)]
196#[cfg(test)]
197mod tests {
198    use super::*;
199
200    const A: [u32; 3] = [1, 2, 3];
201    const B: [u32; 3] = [4, 5, 6];
202    const C: [u32; 2] = [4, 5];
203
204    #[test]
205    fn test_simple_concat() {
206        let d = concat_arrays!(A, B);
207        const D: [u32; concat_arrays_size!(A, B)] = concat_arrays!(A, B);
208        assert_eq!([1, 2, 3, 4, 5, 6], D);
209        assert_eq!([1, 2, 3, 4, 5, 6], d);
210    }
211
212    #[test]
213    fn test_simple_split() {
214        let d: [u32; 6] = concat_arrays!(A, B);
215        const D: [u32; 6] = concat_arrays!(A, B);
216
217        const A_B: ([u32; 3], [u32; 3]) = split_array!(D, A.len(), B.len());
218
219        assert_eq!((A, B), A_B);
220        assert_eq!((A, B), split_array!(d, 3, 3));
221        assert_eq!(([1], [2, 3, 4, 5, 6]), split_array!(d, 1, 5));
222        assert_eq!(([1, 2, 3, 4, 5], [6]), split_array!(d, 5, 1));
223        assert_eq!(([1], [2, 3, 4, 5], [6]), split_array!(d, 1, 4, 1));
224        assert_eq!(([1], [2, 3], [4, 5, 6]), split_array!(d, 1, 2, 3));
225        assert_eq!(
226            ([1], [2], [3], [4], [5], [6]),
227            split_array!(d, 1, 1, 1, 1, 1, 1)
228        );
229    }
230
231    #[test]
232    fn test_different_sizes() {
233        let e = concat_arrays!(A, C);
234        const E: [u32; concat_arrays_size!(A, C)] = concat_arrays!(A, C);
235        assert_eq!([1, 2, 3, 4, 5], E);
236        assert_eq!([1, 2, 3, 4, 5], e);
237    }
238
239    #[test]
240    fn test_literal_arrays() {
241        let f = concat_arrays!(A, C, [6, 7, 8]);
242        const F: [u32; concat_arrays_size!(A, C, [6, 7, 8])] = concat_arrays!(A, C, [6, 7, 8]);
243        assert_eq!([1, 2, 3, 4, 5, 6, 7, 8], F);
244        assert_eq!([1, 2, 3, 4, 5, 6, 7, 8], f);
245    }
246
247    #[test]
248    fn test_non_const_arrays() {
249        let a = [1, 2, 3];
250        let c = [4, 5];
251        let f = concat_arrays!(a, c, [6, 7, 8]);
252        assert_eq!([1, 2, 3, 4, 5, 6, 7, 8], f);
253    }
254}
array_concat/lib.rs

array_concat/
lib.rs
