generic_array/
arr.rs

1//! Implementation for `arr!` macro.
2
3use super::ArrayLength;
4use core::ops::Add;
5use typenum::U1;
6
7/// Helper trait for `arr!` macro
8pub trait AddLength<T, N: ArrayLength<T>>: ArrayLength<T> {
9    /// Resulting length
10    type Output: ArrayLength<T>;
11}
12
13impl<T, N1, N2> AddLength<T, N2> for N1
14where
15    N1: ArrayLength<T> + Add<N2>,
16    N2: ArrayLength<T>,
17    <N1 as Add<N2>>::Output: ArrayLength<T>,
18{
19    type Output = <N1 as Add<N2>>::Output;
20}
21
22/// Helper type for `arr!` macro
23pub type Inc<T, U> = <U as AddLength<T, U1>>::Output;
24
25#[doc(hidden)]
26#[macro_export]
27macro_rules! arr_impl {
28    (@replace_expr $e:expr) => { 1 };
29    ($T:ty; $N:ty, [$($x:expr),*], []) => ({
30        const __ARR_LENGTH: usize = 0 $(+ $crate::arr_impl!(@replace_expr $x) )*;
31
32        #[inline(always)]
33        fn __do_transmute<T, N: $crate::ArrayLength<T>>(arr: [T; __ARR_LENGTH]) -> $crate::GenericArray<T, N> {
34            unsafe { $crate::transmute(arr) }
35        }
36
37        let _: [(); <$N as $crate::typenum::Unsigned>::USIZE] = [(); __ARR_LENGTH];
38
39        __do_transmute::<$T, $N>([$($x as $T),*])
40    });
41    ($T:ty; $N:ty, [], [$x1:expr]) => (
42        $crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$x1], [])
43    );
44    ($T:ty; $N:ty, [], [$x1:expr, $($x:expr),+]) => (
45        $crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$x1], [$($x),+])
46    );
47    ($T:ty; $N:ty, [$($y:expr),+], [$x1:expr]) => (
48        $crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$($y),+, $x1], [])
49    );
50    ($T:ty; $N:ty, [$($y:expr),+], [$x1:expr, $($x:expr),+]) => (
51        $crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$($y),+, $x1], [$($x),+])
52    );
53}
54
55/// Macro allowing for easy generation of Generic Arrays.
56/// Example: `let test = arr![u32; 1, 2, 3];`
57#[macro_export]
58macro_rules! arr {
59    ($T:ty; $(,)*) => ({
60        unsafe { $crate::transmute::<[$T; 0], $crate::GenericArray<$T, $crate::typenum::U0>>([]) }
61    });
62    ($T:ty; $($x:expr),* $(,)*) => (
63        $crate::arr_impl!($T; $crate::typenum::U0, [], [$($x),*])
64    );
65    ($($x:expr,)+) => (arr![$($x),+]);
66    () => ("""Macro requires a type, e.g. `let array = arr![u32; 1, 2, 3];`")
67}
68
69mod doctests_only {
70    ///
71    /// # With ellision
72    ///
73    /// Testing that lifetimes aren't transmuted when they're ellided.
74    ///
75    /// ```compile_fail
76    /// #[macro_use] extern crate generic_array;
77    /// fn main() {
78    ///    fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'static A {
79    ///        arr![&A; a][0]
80    ///    }
81    /// }
82    /// ```
83    ///
84    /// ```rust
85    /// #[macro_use] extern crate generic_array;
86    /// fn main() {
87    ///    fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'a A {
88    ///        arr![&A; a][0]
89    ///    }
90    /// }
91    /// ```
92    ///
93    /// # Without ellision
94    ///
95    /// Testing that lifetimes aren't transmuted when they're specified explicitly.
96    ///
97    /// ```compile_fail
98    /// #[macro_use] extern crate generic_array;
99    /// fn main() {
100    ///    fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'static A {
101    ///        arr![&'a A; a][0]
102    ///    }
103    /// }
104    /// ```
105    ///
106    /// ```compile_fail
107    /// #[macro_use] extern crate generic_array;
108    /// fn main() {
109    ///    fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'static A {
110    ///        arr![&'static A; a][0]
111    ///    }
112    /// }
113    /// ```
114    ///
115    /// ```rust
116    /// #[macro_use] extern crate generic_array;
117    /// fn main() {
118    ///    fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'a A {
119    ///        arr![&'a A; a][0]
120    ///    }
121    /// }
122    /// ```
123    #[allow(dead_code)]
124    pub enum DocTests {}
125}
generic_array/arr.rs

generic_array/
arr.rs
