diff options
| -rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0517.md | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0517.md b/compiler/rustc_error_codes/src/error_codes/E0517.md index ae802245bd1..5354a08bf31 100644 --- a/compiler/rustc_error_codes/src/error_codes/E0517.md +++ b/compiler/rustc_error_codes/src/error_codes/E0517.md @@ -25,14 +25,17 @@ impl Foo { These attributes do not work on typedefs, since typedefs are just aliases. Representations like `#[repr(u8)]`, `#[repr(i64)]` are for selecting the -discriminant size for enums with no data fields on any of the variants, e.g. -`enum Color {Red, Blue, Green}`, effectively setting the size of the enum to -the size of the provided type. Such an enum can be cast to a value of the same -type as well. In short, `#[repr(u8)]` makes the enum behave like an integer -with a constrained set of allowed values. +discriminant size for enums. For enums with no data fields on any of the +variants, e.g. `enum Color {Red, Blue, Green}`, this effectively sets the size +of the enum to the size of the provided type. Such an enum can be cast to a +value of the same type as well. In short, `#[repr(u8)]` makes a field-less enum +behave like an integer with a constrained set of allowed values. -Only field-less enums can be cast to numerical primitives, so this attribute -will not apply to structs. +For a description of how `#[repr(C)]` and representations like `#[repr(u8)]` +affect the layout of enums with data fields, see [RFC 2195][rfc2195]. + +Only field-less enums can be cast to numerical primitives. Representations like +`#[repr(u8)]` will not apply to structs. `#[repr(packed)]` reduces padding to make the struct size smaller. The representation of enums isn't strictly defined in Rust, and this attribute @@ -42,3 +45,5 @@ won't work on enums. types (i.e., `u8`, `i32`, etc) a representation that permits vectorization via SIMD. This doesn't make much sense for enums since they don't consist of a single list of data. + +[rfc2195]: https://github.com/rust-lang/rfcs/blob/master/text/2195-really-tagged-unions.md |