Merge pull request #500 from CosmWasm/461-uniqueindex-range_de

range_de / prefix_de impls for Map-like structs

packages/storage-plus/README.md

@@ -613,3 +613,21 @@ Another example that is similar, but returning only the `token_id`s, using the `
         .collect();
 ```
 Now `pks` contains `token_id` values (as `Vec<u8>`s) for the given `owner`.
+
+### Index keys deserialization
+
+To deserialize keys of indexes (using the `*_de` functions), there are currently some requirements / limitations:
+
+- For `UniqueIndex`: The primary key (`PK`) type needs to be specified, in order to deserialize the primary key to it.
+This generic type comes with a default of `()`, which means that no deserialization / data will be provided
+for the primary key. This is for backwards compatibility with the current `UniqueIndex` impl. It can also come handy
+in cases you don't need the primary key, and are interested only in the deserialized value.
+
+- For `MultiIndex`: The last element of the index tuple must be specified with the type you want it to be deserialized.
+That is, the last tuple element serves as a marker for the deserialization type (in the same way `PK` does it in
+`UniqueIndex`).
+
+- There are currently some inconsistencies in the values that are returned for the different index keys. `MultiIndex`
+returns a tuple with the remaining part of the index key along with the primary key, whereas `UniqueIndex` returns only
+the primary key. This will be changed in the future (See https://github.com/CosmWasm/cw-plus/issues/532) for consistency
+and compatibility with the base `Map` type behaviour.