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//! Implementation for `arr!` macro.
use super::ArrayLength;
use core::ops::Add;
use typenum::U1;
/// Helper trait for `arr!` macro
pub trait AddLength<T, N: ArrayLength<T>>: ArrayLength<T> {
/// Resulting length
type Output: ArrayLength<T>;
}
impl<T, N1, N2> AddLength<T, N2> for N1
where
N1: ArrayLength<T> + Add<N2>,
N2: ArrayLength<T>,
<N1 as Add<N2>>::Output: ArrayLength<T>,
{
type Output = <N1 as Add<N2>>::Output;
}
/// Helper type for `arr!` macro
pub type Inc<T, U> = <U as AddLength<T, U1>>::Output;
#[doc(hidden)]
#[macro_export]
macro_rules! arr_impl {
(@replace_expr $e:expr) => { 1 };
($T:ty; $N:ty, [$($x:expr),*], []) => ({
const __ARR_LENGTH: usize = 0 $(+ $crate::arr_impl!(@replace_expr $x) )*;
#[inline(always)]
fn __do_transmute<T, N: $crate::ArrayLength<T>>(arr: [T; __ARR_LENGTH]) -> $crate::GenericArray<T, N> {
unsafe { $crate::transmute(arr) }
}
let _: [(); <$N as $crate::typenum::Unsigned>::USIZE] = [(); __ARR_LENGTH];
__do_transmute::<$T, $N>([$($x as $T),*])
});
($T:ty; $N:ty, [], [$x1:expr]) => (
$crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$x1], [])
);
($T:ty; $N:ty, [], [$x1:expr, $($x:expr),+]) => (
$crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$x1], [$($x),+])
);
($T:ty; $N:ty, [$($y:expr),+], [$x1:expr]) => (
$crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$($y),+, $x1], [])
);
($T:ty; $N:ty, [$($y:expr),+], [$x1:expr, $($x:expr),+]) => (
$crate::arr_impl!($T; $crate::arr::Inc<$T, $N>, [$($y),+, $x1], [$($x),+])
);
}
/// Macro allowing for easy generation of Generic Arrays.
/// Example: `let test = arr![u32; 1, 2, 3];`
#[macro_export]
macro_rules! arr {
($T:ty; $(,)*) => ({
unsafe { $crate::transmute::<[$T; 0], $crate::GenericArray<$T, $crate::typenum::U0>>([]) }
});
($T:ty; $($x:expr),* $(,)*) => (
$crate::arr_impl!($T; $crate::typenum::U0, [], [$($x),*])
);
($($x:expr,)+) => (arr![$($x),+]);
() => ("""Macro requires a type, e.g. `let array = arr![u32; 1, 2, 3];`")
}
mod doctests_only {
///
/// # With ellision
///
/// Testing that lifetimes aren't transmuted when they're ellided.
///
/// ```compile_fail
/// #[macro_use] extern crate generic_array;
/// fn main() {
/// fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'static A {
/// arr![&A; a][0]
/// }
/// }
/// ```
///
/// ```rust
/// #[macro_use] extern crate generic_array;
/// fn main() {
/// fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'a A {
/// arr![&A; a][0]
/// }
/// }
/// ```
///
/// # Without ellision
///
/// Testing that lifetimes aren't transmuted when they're specified explicitly.
///
/// ```compile_fail
/// #[macro_use] extern crate generic_array;
/// fn main() {
/// fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'static A {
/// arr![&'a A; a][0]
/// }
/// }
/// ```
///
/// ```compile_fail
/// #[macro_use] extern crate generic_array;
/// fn main() {
/// fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'static A {
/// arr![&'static A; a][0]
/// }
/// }
/// ```
///
/// ```rust
/// #[macro_use] extern crate generic_array;
/// fn main() {
/// fn unsound_lifetime_extension<'a, A>(a: &'a A) -> &'a A {
/// arr![&'a A; a][0]
/// }
/// }
/// ```
#[allow(dead_code)]
pub enum DocTests {}
}
|
