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/// Asserts that types are equal in alignment.
///
/// This is useful when ensuring that pointer arithmetic is done correctly, or
/// when [FFI] requires a type to have the same alignment as some foreign type.
///
/// # Examples
///
/// A `usize` has the same alignment as any pointer type:
///
/// ```
/// # #[macro_use] extern crate static_assertions; fn main() {}
/// assert_eq_align!(usize, *const u8, *mut u8);
/// ```
///
/// The following passes because `[i32; 4]` has the same alignment as `i32`:
///
/// ```
/// # #[macro_use] extern crate static_assertions; fn main() {}
/// assert_eq_align!([i32; 4], i32);
/// ```
///
/// The following example fails to compile because `i32x4` explicitly has 4
/// times the alignment as `[i32; 4]`:
///
/// ```compile_fail
/// # #[macro_use] extern crate static_assertions; fn main() {}
/// # #[allow(non_camel_case_types)]
/// #[repr(align(16))]
/// struct i32x4([i32; 4]);
///
/// assert_eq_align!(i32x4, [i32; 4]);
/// ```
///
/// [FFI]: https://en.wikipedia.org/wiki/Foreign_function_interface
#[macro_export]
macro_rules! assert_eq_align {
($x:ty, $($xs:ty),+ $(,)?) => {
const _: fn() = || {
// Assigned instance must match the annotated type or else it will
// fail to compile
use $crate::_core::mem::align_of;
$(let _: [(); align_of::<$x>()] = [(); align_of::<$xs>()];)+
};
};
}
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