1/// Asserts that types are equal in alignment.
2///
3/// This is useful when ensuring that pointer arithmetic is done correctly, or
4/// when [FFI] requires a type to have the same alignment as some foreign type.
5///
6/// # Examples
7///
8/// A `usize` has the same alignment as any pointer type:
9///
10/// ```
11/// # #[macro_use] extern crate static_assertions; fn main() {}
12/// assert_eq_align!(usize, *const u8, *mut u8);
13/// ```
14///
15/// The following passes because `[i32; 4]` has the same alignment as `i32`:
16///
17/// ```
18/// # #[macro_use] extern crate static_assertions; fn main() {}
19/// assert_eq_align!([i32; 4], i32);
20/// ```
21///
22/// The following example fails to compile because `i32x4` explicitly has 4
23/// times the alignment as `[i32; 4]`:
24///
25/// ```compile_fail
26/// # #[macro_use] extern crate static_assertions; fn main() {}
27/// # #[allow(non_camel_case_types)]
28/// #[repr(align(16))]
29/// struct i32x4([i32; 4]);
30///
31/// assert_eq_align!(i32x4, [i32; 4]);
32/// ```
33///
34/// [FFI]: https://en.wikipedia.org/wiki/Foreign_function_interface
35#[macro_export]
36macro_rules! assert_eq_align {
37 ($x:ty, $($xs:ty),+ $(,)?) => {
38 const _: fn() = || {
39 // Assigned instance must match the annotated type or else it will
40 // fail to compile
41 use $crate::_core::mem::align_of;
42 $(let _: [(); align_of::<$x>()] = [(); align_of::<$xs>()];)+
43 };
44 };
45}
46

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