storey: document Column

src/pages/storey/containers/column.mdx

@@ -5,3 +5,132 @@ tags: ["storey", "containers"]
 import { Callout } from "nextra/components";
 
 # Column
+
+A [`Column`] is a collection of items indexed by auto-incrementing `u32` keys.
+This might sound similar to a relational database table; in fact, it is a good analogy.
+
+A [`Column`] makes it efficient to push items to it and access the last element.
+
+<Callout>
+It should be noted that in a future version indexing will start at `1`, not `0`.
+
+This change will also break existing contracts that rely on the current `Column` implementation!
+</Callout>
+
+## Examples
+
+### Storing a message log
+
+Let's say you want to store a log of messages. You can do this with a `Column<String>`.
+
+```rust template="storage" showLineNumbers {6,8,10,12}
+use cw_storey::containers::Column;
+use cw_storey::CwStorage;
+
+const MESSAGES_IX: u8 = 1;
+
+let messages: Column<String> = Column::new(MESSAGES_IX);
+let mut cw_storage = CwStorage(&mut storage);
+let mut access = messages.access(&mut cw_storage);
+
+access.push(&"Hello, world!".to_string()).unwrap();
+
+assert_eq!(access.get(0).unwrap(), Some("Hello, world!".to_string()));
+```
+
+- _line 6:_ Here we construct the `Column` facade. The constructor takes a key, which is the prefix of
+  the keys in the underlying storage backend.
+- _line 8:_ The [`access`] method returns a [`ColumnAccess`] entity, which allows manipulating the column.
+- _line 10:_ Here we push a message to the column.
+- _line 12:_ We check that the message is stored correctly.
+
+#### Iterating over the messages
+
+As with [`Map`], we can iterate over all messages.
+
+```rust template="storage" showLineNumbers {4, 17}
+use cw_storey::containers::{Column, Item};
+use cw_storey::CwStorage;
+
+use storey::containers::IterableAccessor as _;
+
+const MESSAGES_IX: u8 = 1;
+
+let messages: Column<String> = Column::new(MESSAGES_IX);
+let mut cw_storage = CwStorage(&mut storage);
+let mut access = messages.access(&mut cw_storage);
+
+// populate the column
+access.push(&"Hello, world!".to_string()).unwrap();
+access.push(&"My name is Bob.".to_string()).unwrap();
+access.push(&"Hell is empty and all the devils are here.".to_string()).unwrap();
+
+let messages: Vec<_> = access.pairs().collect::<Result<_, _>>().unwrap();
+
+assert_eq!(messages, vec![
+    (0, "Hello, world!".to_string()),
+    (1, "My name is Bob.".to_string()),
+    (2, "Hell is empty and all the devils are here.".to_string()),
+]);
+```
+
+- _line 4:_ We import the `IterableAccessor` trait to use iteration methods.
+- _line 17:_ The `pairs` method produces an iterator
+    over tuples of `(index, value)`. In this case, we collect the iterator into a `Vec` for ease of making our assertion later.
+
+Similarly to [`Map`], you can use the [`keys`], [`values`], and [`pairs`] methods to iterate over the items.
+
+#### Bounded iteration
+
+If you want to perform bounded iteration, it is possible.
+This time you need the [`BoundedIterableAccessor`] trait, and the relevant methods are
+[`bounded_pairs`], [`bounded_keys`], and [`bounded_values`].
+
+The following example is the same as the previous one except for the bounds
+found in line 17, and the limited results.
+
+<Callout>
+Currently, the lower bound is inclusive, and the upper bound is exclusive.
+
+This will change in a future version, where you'll be able to choose between inclusive and exclusive bounds as suits you.
+</Callout>
+
+```rust template="storage" showLineNumbers {4, 17}
+use cw_storey::containers::{Column, Item};
+use cw_storey::CwStorage;
+
+use storey::containers::BoundedIterableAccessor as _;
+
+const MESSAGES_IX: u8 = 1;
+
+let messages: Column<String> = Column::new(MESSAGES_IX);
+let mut cw_storage = CwStorage(&mut storage);
+let mut access = messages.access(&mut cw_storage);
+
+// populate the column
+access.push(&"Hello, world!".to_string()).unwrap();
+access.push(&"My name is Bob.".to_string()).unwrap();
+access.push(&"Hell is empty and all the devils are here.".to_string()).unwrap();
+
+let messages: Vec<_> = access.bounded_pairs(Some(0), Some(2)).collect::<Result<_, _>>().unwrap();
+
+assert_eq!(messages, vec![
+    (0, "Hello, world!".to_string()),
+    (1, "My name is Bob.".to_string()),
+]);
+```
+
+[`Column`]: https://docs.rs/storey/latest/storey/containers/struct.Column.html
+[`access`]: https://docs.rs/storey/latest/storey/containers/struct.Column.html#method.access
+[`ColumnAccess`]: https://docs.rs/storey/latest/storey/containers/struct.ColumnAccess.html
+[`keys`]: https://docs.rs/storey/latest/storey/containers/struct.ColumnAccess.html#method.keys
+[`values`]: https://docs.rs/storey/latest/storey/containers/struct.ColumnAccess.html#method.values
+[`pairs`]: https://docs.rs/storey/latest/storey/containers/struct.ColumnAccess.html#method.pairs
+[`Map`]: https://docs.rs/storey/latest/storey/containers/struct.Map.html
+[`MapAccess`]: https://docs.rs/storey/latest/storey/containers/struct.MapAccess.html
+[`ItemAccess`]: https://docs.rs/storey/latest/storey/containers/struct.ItemAccess.html
+[`IterableAccessor`]: https://docs.rs/storey/latest/storey/containers/trait.IterableAccessor.html
+[`BoundedIterableAccessor`]: https://docs.rs/storey/latest/storey/containers/trait.BoundedIterableAccessor.html
+[`bounded_pairs`]: https://docs.rs/storey/latest/storey/containers/trait.BoundedIterableAccessor.html#method.bounded_pairs
+[`bounded_keys`]: https://docs.rs/storey/latest/storey/containers/trait.BoundedIterableAccessor.html#method.bounded_keys
+[`bounded_values`]: https://docs.rs/storey/latest/storey/containers/trait.BoundedIterableAccessor.html#method.bounded_values