//! 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 {} }