Add Signal::modify to mutate a value

examples/todomvc/src/main.rs

@@ -52,30 +52,15 @@ pub struct AppState {
 
 impl AppState {
     fn add_todo(&self, title: String) {
-        self.todos.set(
-            self.todos
-                .get()
-                .as_ref()
-                .clone()
-                .into_iter()
-                .chain(Some(create_rc_signal(Todo {
-                    title,
-                    completed: false,
-                    id: Uuid::new_v4(),
-                })))
-                .collect(),
-        )
+        self.todos.modify().push(create_rc_signal(Todo {
+            title,
+            completed: false,
+            id: Uuid::new_v4(),
+        }))
     }
 
     fn remove_todo(&self, id: Uuid) {
-        self.todos.set(
-            self.todos
-                .get()
-                .iter()
-                .filter(|todo| todo.get().id != id)
-                .cloned()
-                .collect(),
-        );
+        self.todos.modify().retain(|todo| todo.get().id != id);
     }
 
     fn todos_left(&self) -> usize {
@@ -110,14 +95,7 @@ impl AppState {
     }
 
     fn clear_completed(&self) {
-        self.todos.set(
-            self.todos
-                .get()
-                .iter()
-                .filter(|todo| !todo.get().completed)
-                .cloned()
-                .collect(),
-        );
+        self.todos.modify().retain(|todo| !todo.get().completed);
     }
 }
 
@@ -456,7 +434,7 @@ pub fn Footer<G: Html>(cx: Scope) -> View<G> {
                     }
                 }
             } else {
-                View::empty()
+                view! { cx, }
             })
         }
     }

packages/sycamore-reactive/src/signal.rs

@@ -2,7 +2,7 @@
 
 use std::fmt::{Debug, Display, Formatter};
 use std::hash::Hash;
-use std::ops::{AddAssign, Deref, DivAssign, MulAssign, SubAssign};
+use std::ops::{AddAssign, Deref, DerefMut, DivAssign, MulAssign, SubAssign};
 
 use crate::effect::EFFECTS;
 use crate::*;
@@ -246,6 +246,49 @@ impl<T> Signal<T> {
     }
 }
 
+/// A mutable reference for modifying a [`Signal`].
+///
+/// Construct this using the [`Signal::modify()`] method.
+pub struct Modify<'a, T>(Option<T>, &'a Signal<T>);
+
+impl<'a, T> Deref for Modify<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        self.0.as_ref().unwrap()
+    }
+}
+impl<'a, T> DerefMut for Modify<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.0.as_mut().unwrap()
+    }
+}
+
+/// When the mutable handle is dropped, update the [`Signal`].
+impl<T> Drop for Modify<'_, T> {
+    fn drop(&mut self) {
+        self.1.set(self.0.take().unwrap())
+    }
+}
+
+impl<T: Clone> Signal<T> {
+    /// Return a mutable handle to make it easier to mutate the inner value.
+    /// This requires the inner type to implement [`Clone`].
+    ///
+    /// # Example
+    /// ```
+    /// # use sycamore_reactive::*;
+    /// # create_scope_immediate(|cx| {
+    /// let state = create_signal(cx, "Hello ".to_string());
+    /// state.modify().push_str("World!");
+    /// assert_eq!(*state.get(), "Hello World!");
+    /// # });
+    /// ```
+    pub fn modify(&self) -> Modify<T> {
+        Modify(Some(self.value.borrow().as_ref().clone()), self)
+    }
+}
+
 impl<T: Default> Signal<T> {
     /// Take the current value out and replace it with the default value.
     ///
@@ -662,4 +705,19 @@ mod tests {
             assert_eq!(*counter.get(), 5);
         });
     }
+
+    #[test]
+    fn signal_modify() {
+        create_scope_immediate(|cx| {
+            let signal = create_signal(cx, "Hello ".to_string());
+            let counter = create_signal(cx, 0);
+            create_effect(cx, || {
+                signal.track();
+                counter.set(*counter.get_untracked() + 1);
+            });
+            signal.modify().push_str("World!");
+            assert_eq!(*signal.get(), "Hello World!");
+            assert_eq!(*counter.get(), 2);
+        });
+    }
 }

packages/sycamore-router/Cargo.toml

@@ -15,7 +15,7 @@ version = "0.8.0-beta.3"
 
 [dependencies]
 sycamore = { path = "../sycamore", version = "0.8.0-beta.3" }
-sycamore-router-macro = { path = "../sycamore-router-macro", version = "0.8.0-beta.3" }
+sycamore-router-macro = { path = "../sycamore-router-macro", version = "=0.8.0-beta.3" }
 wasm-bindgen = "0.2.79"
 
 [dependencies.web-sys]

packages/sycamore/Cargo.toml

@@ -19,7 +19,7 @@ js-sys = "0.3.56"
 once_cell = { version = "1.10.0", optional = true }
 paste = "1.0.6"
 sycamore-futures = { path = "../sycamore-futures", version = "0.8.0-beta.3", optional = true }
-sycamore-macro = { path = "../sycamore-macro", version = "0.8.0-beta.3" }
+sycamore-macro = { path = "../sycamore-macro", version = "=0.8.0-beta.3" }
 sycamore-reactive = { path = "../sycamore-reactive", version = "0.8.0-beta.3" }
 wasm-bindgen = "0.2.79"
 wasm-bindgen-futures = { version = "0.4.29", optional = true }