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_posts/2015-12-09-modifying-page-tables.md
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@@ -340,14 +340,14 @@ 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 `Level4` in exported types, they need to be public as well.
To differentiate the P1 table from the other tables, we introduce a `HierachicalLevel` trait, which is a subtrait of `TableLevel`. But we implement it only for the levels 4, 3, and 2: 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 ```rust
trait HierachicalLevel: TableLevel {} trait HierarchicalLevel: TableLevel {}
impl HierachicalLevel for Level4 {} impl HierarchicalLevel for Level4 {}
impl HierachicalLevel for Level3 {} impl HierarchicalLevel for Level3 {}
impl HierachicalLevel for Level2 {} impl HierarchicalLevel for Level2 {}
``` ```
Now we add the level parameter to the `Table` type: Now we add the level parameter to the `Table` type:
@@ -374,7 +374,7 @@ impl<L> Table<L> where L: TableLevel
pub fn zero(&mut self) {...} pub fn zero(&mut self) {...}
} }
impl<L> Table<L> where L: HierachicalLevel impl<L> Table<L> where L: HierarchicalLevel
{ {
pub fn next_table(&self, index: usize) -> Option<&Table<???>> {...} pub fn next_table(&self, index: usize) -> Option<&Table<???>> {...}
@@ -391,22 +391,22 @@ Now the `next_table` methods are only available for P4, P3, and P2 tables. But t
For a P4 table we would like to return a `Table<Level3>`, for a P3 table a `Table<Level2>`, and for a P2 table a `Table<Level1>`. So we want to return a table of the _next level_. For a P4 table we would like to return a `Table<Level3>`, for a P3 table a `Table<Level2>`, and for a P2 table a `Table<Level1>`. So we want to return a table of the _next level_.
We can define the next level by adding an associated type to the `HierachicalLevel` trait: We can define the next level by adding an associated type to the `HierarchicalLevel` trait:
```rust ```rust
trait HierachicalLevel: TableLevel { trait HierarchicalLevel: TableLevel {
type NextLevel: TableLevel; type NextLevel: TableLevel;
} }
impl HierachicalLevel for Level4 { impl HierarchicalLevel for Level4 {
type NextLevel = Level3; type NextLevel = Level3;
} }
impl HierachicalLevel for Level3 { impl HierarchicalLevel for Level3 {
type NextLevel = Level2; type NextLevel = Level2;
} }
impl HierachicalLevel for Level2 { impl HierarchicalLevel for Level2 {
type NextLevel = Level1; type NextLevel = Level1;
} }
``` ```