1 files changed, 60 insertions, 0 deletions
diff --git a/native/src/widget/operation.rs b/native/src/widget/operation.rs
new file mode 100644
index 00000000..ef636aa2
--- /dev/null
+++ b/native/src/widget/operation.rs
@@ -0,0 +1,60 @@
+//! Query or update internal widget state.
+pub mod focusable;
+pub mod scrollable;
+
+pub use focusable::Focusable;
+pub use scrollable::Scrollable;
+
+use crate::widget::Id;
+
+use std::fmt;
+
+/// A piece of logic that can traverse the widget tree of an application in
+/// order to query or update some widget state.
+pub trait Operation<T> {
+    /// Operates on a widget that contains other widgets.
+    ///
+    /// The `operate_on_children` function can be called to return control to
+    /// the widget tree and keep traversing it.
+    fn container(
+        &mut self,
+        id: Option<&Id>,
+        operate_on_children: &mut dyn FnMut(&mut dyn Operation<T>),
+    );
+
+    /// Operates on a widget that can be focused.
+    fn focusable(&mut self, _state: &mut dyn Focusable, _id: Option<&Id>) {}
+
+    /// Operates on a widget that can be scrolled.
+    fn scrollable(&mut self, _state: &mut dyn Scrollable, _id: Option<&Id>) {}
+
+    /// Finishes the [`Operation`] and returns its [`Outcome`].
+    fn finish(&self) -> Outcome<T> {
+        Outcome::None
+    }
+}
+
+/// The result of an [`Operation`].
+pub enum Outcome<T> {
+    /// The [`Operation`] produced no result.
+    None,
+
+    /// The [`Operation`] produced some result.
+    Some(T),
+
+    /// The [`Operation`] needs to be followed by another [`Operation`].
+    Chain(Box<dyn Operation<T>>),
+}
+
+impl<T> fmt::Debug for Outcome<T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::None => write!(f, "Outcome::None"),
+            Self::Some(output) => write!(f, "Outcome::Some({:?})", output),
+            Self::Chain(_) => write!(f, "Outcome::Chain(...)"),
+        }
+    }
+}