Crates.io | elain |
lib.rs | elain |
version | 0.3.0 |
source | src |
created_at | 2021-04-08 18:27:53.824305 |
updated_at | 2021-04-13 18:52:41.694867 |
description | Set a type's minimum alignment with const generics. |
homepage | |
repository | |
max_upload_size | |
id | 380988 |
size | 14,771 |
Set the minimum alignments of types using const generics, rather
than #[repr(align(N))]
.
The type Align<N>
is a zero-sized-type with alignment
equal to N
:
use elain::Align;
use core::mem::{align_of, align_of_val};
assert_eq!(align_of::<Align<1>>(), 1);
assert_eq!(align_of::<Align<2>>(), 2);
assert_eq!(align_of::<Align<4>>(), 4);
const FOO_ALIGN: usize = 8;
#[repr(C)]
struct Foo {
_align: Align<FOO_ALIGN>,
}
let foo: Foo = Foo { _align: Align::NEW };
assert_eq!(align_of_val(&foo), 8);
Valid alignments are powers of two less-than-or-equal to 228.
Supplying an invalid alignment to [Align
] is a type error:
use elain::Align;
struct Foo(Align<3>); // Compile Error
Because only some integers are valid alignments, supplying the alignment of a type generically requires some extra work:
use elain::Align;
struct Foo<const N: usize> {
_align: Align<N>,
}
To resolve this error, add a where
bound like so, using the
[Alignment
] trait to check that Align<N>
is valid.
use elain::{Align, Alignment};
use core::mem::align_of;
struct Foo<const MIN_ALIGNMENT: usize>
where
Align<MIN_ALIGNMENT>: Alignment
{
_align: Align<MIN_ALIGNMENT>,
bar: u8,
baz: u16,
}
assert_eq!(align_of::<Foo<1>>(), 2);
assert_eq!(align_of::<Foo<2>>(), 2);
assert_eq!(align_of::<Foo<4>>(), 4);