add #[repr(C)] to the union

nikomatsakis · nikomatsakis · commit ffe8aa676e80 · 2018-12-20T12:13:01.000-05:00
diff --git a/reference/src/representation/enums.md b/reference/src/representation/enums.md
@@ -180,6 +180,7 @@ This will be laid out equivalently to the following more
 complex Rust types:
 
 ```
+#[repr(C)]
 union TwoCasesRepr {
     A: TwoCasesVariantA,
     B: TwoCasesVariantB,
