use a repr(C) struct with a [T; 0] as first field for alignment

cehteh · cehteh · commit dd95b985b98a · 2025-04-05T20:13:49.000+02:00
This is a bit cleaner than using a union For discussion about see: kazcw/alignas#1 (comment)
diff --git a/src/lib.rs b/src/lib.rs
@@ -51,10 +51,11 @@ struct HeaderVecHeader<H> {
     len: usize,
 }
 
-// This union will be properly aligned and sized to store headers followed by T's.
-union AlignedHeader<H, T> {
-    _header: ManuallyDrop<HeaderVecHeader<H>>,
-    _data: ManuallyDrop<[T; 0]>,
+// This struct will be properly aligned and sized to store headers followed by T's.
+#[repr(C)]
+struct AlignedHeader<H, T> {
+    align: [T; 0],
+    header: HeaderVecHeader<H>,
 }
 
 /// A vector with a header of your choosing behind a thin pointer

Original file line number	Diff line number	Diff line change
`@@ -51,10 +51,11 @@ struct HeaderVecHeader<H> {`
`51`	`51`	`len: usize,`
`52`	`52`	`}`
`53`	`53`
`54`		`-// This union will be properly aligned and sized to store headers followed by T's.`
`55`		`-union AlignedHeader<H, T> {`
`56`		`- _header: ManuallyDrop<HeaderVecHeader<H>>,`
`57`		`- _data: ManuallyDrop<[T; 0]>,`
	`54`	`+// This struct will be properly aligned and sized to store headers followed by T's.`
	`55`	`+#[repr(C)]`
	`56`	`+struct AlignedHeader<H, T> {`
	`57`	`+ align: [T; 0],`
	`58`	`+ header: HeaderVecHeader<H>,`
`58`	`59`	`}`
`59`	`60`
`60`	`61`	`/// A vector with a header of your choosing behind a thin pointer`