git.delta.rocks / unique-network / refs/commits / 03866db9b34b

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+# struct-versioning
+
+The crate contains procedural macros for versioning data structures.
+Macros [`versioned`] generate versioned variants of a struct.
+
+Example:
+```
+# use struct_versioning::versioned;
+#[versioned(version = 5, first_version = 2)]
+struct Example {}
+
+// versioned macro will generate suffixed versions of example struct,
+// starting from `Version{first_version or 1}` to `Version{version}` inclusive
+let _ver2 = ExampleVersion2 {};
+let _ver3 = ExampleVersion3 {};
+let _ver4 = ExampleVersion4 {};
+let _ver5 = ExampleVersion5 {};
+
+// last version will also be aliased with original struct name
+let _orig: Example = ExampleVersion5 {};
+
+#[versioned(version = 2, upper)]
+#[derive(PartialEq, Debug)]
+struct Upper {
+    #[version(..2)]
+    removed: u32,
+    #[version(2.., upper(10))]
+    added: u32,
+
+    #[version(..2)]
+    retyped: u32,
+    #[version(2.., upper(retyped as u64))]
+    retyped: u64,
+}
+
+// #[version] attribute on field allows to specify, in which versions of structs this field should present
+// versions here works as standard rust ranges, start is inclusive, end is exclusive
+let _up1 = UpperVersion1 {removed: 1, retyped: 0};
+let _up2 = UpperVersion2 {added: 1, retyped: 0};
+
+// and upper() allows to specify, which value should be assigned to this field in `From<OldVersion>` impl
+assert_eq!(
+    UpperVersion2::from(UpperVersion1 {removed: 0, retyped: 6}),
+    UpperVersion2 {added: 10, retyped: 6},
+);
+```
+
+In this case, the upgrade is described in `on_runtime_upgrade` using the `translate_values` substrate feature
+
+```ignore
+#[pallet::hooks]
+impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
+    fn on_runtime_upgrade() -> Weight {
+        if StorageVersion::get::<Pallet<T>>() < StorageVersion::new(1) {
+            <TokenData<T>>::translate_values::<ItemDataVersion1, _>(|v| {
+                Some(<ItemDataVersion2>::from(v))
+            })
+        }
+        0
+    }
+}
+```