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2016-02-24 16:42:48 +00:00
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_posts/2015-12-09-modifying-page-tables.md
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@@ -345,21 +345,21 @@ To model the levels we use a trait and empty enums:
pub trait TableLevel {}
pub enum Level4 {}
enum Level3 {}
enum Level2 {}
enum Level1 {}
pub enum Level3 {}
pub enum Level2 {}
pub enum Level1 {}
impl TableLevel for Level4 {}
impl TableLevel for Level3 {}
impl TableLevel for Level2 {}
impl TableLevel for Level1 {}
```
An empty enum has size zero and disappears completely after compiling. Unlike an empty struct, it's not possible to instantiate an empty enum. Since we will use `TableLevel` and `Level4` in exported types, they need to be public as well.
An empty enum has size zero and disappears completely after compiling. Unlike an empty struct, it's not possible to instantiate an empty enum. Since we will use `TableLevel` and the table levels in exported types, they need to be public.
To differentiate the P1 table from the other tables, we introduce a `HierarchicalLevel` trait, which is a subtrait of `TableLevel`. But we implement it only for the levels 4, 3, and 2:
```rust
trait HierarchicalLevel: TableLevel {}
pub trait HierarchicalLevel: TableLevel {}
impl HierarchicalLevel for Level4 {}
impl HierarchicalLevel for Level3 {}