chore: checkpoint before Python removal

vendor/valuable/examples/hello_world.rs

@@ -0,0 +1,68 @@
+use valuable::*;
+
+struct HelloWorld {
+    hello: &'static str,
+    world: World,
+}
+
+struct World {
+    answer: usize,
+}
+
+static HELLO_WORLD_FIELDS: &[NamedField<'static>] =
+    &[NamedField::new("hello"), NamedField::new("world")];
+
+impl Structable for HelloWorld {
+    fn definition(&self) -> StructDef<'_> {
+        StructDef::new_static("HelloWorld", Fields::Named(HELLO_WORLD_FIELDS))
+    }
+}
+
+impl Valuable for HelloWorld {
+    fn as_value(&self) -> Value<'_> {
+        Value::Structable(self)
+    }
+
+    fn visit(&self, v: &mut dyn Visit) {
+        v.visit_named_fields(&NamedValues::new(
+            HELLO_WORLD_FIELDS,
+            &[Value::String(self.hello), Value::Structable(&self.world)],
+        ));
+    }
+}
+
+static WORLD_FIELDS: &[NamedField<'static>] = &[NamedField::new("answer")];
+
+impl Valuable for World {
+    fn as_value(&self) -> Value<'_> {
+        Value::Structable(self)
+    }
+
+    fn visit(&self, v: &mut dyn Visit) {
+        v.visit_named_fields(&NamedValues::new(
+            WORLD_FIELDS,
+            &[Value::Usize(self.answer)],
+        ));
+    }
+}
+
+impl Structable for World {
+    fn definition(&self) -> StructDef<'_> {
+        StructDef::new_static("World", Fields::Named(WORLD_FIELDS))
+    }
+}
+
+fn main() {
+    let hello_world = HelloWorld {
+        hello: "wut",
+        world: World { answer: 42 },
+    };
+
+    let value = Value::Structable(&hello_world);
+    println!("{:#?}", value);
+
+    let slice = &[1, 2, 3][..];
+
+    let value = &slice as &dyn Valuable;
+    println!("{:?}", value);
+}