feat: add write function to State (#45)

packages/iocraft/src/hooks/use_state.rs

@@ -6,7 +6,7 @@ use core::{
     pin::Pin,
     task::{Context, Poll, Waker},
 };
-use generational_box::{AnyStorage, GenerationalBox, Owner, SyncStorage};
+use generational_box::{AnyStorage, BorrowError, GenerationalBox, Owner, SyncStorage};
 
 mod private {
     pub trait Sealed {}
@@ -115,6 +115,38 @@ impl<'a, T: 'static> ops::Deref for StateRef<'a, T> {
     }
 }
 
+/// A mutable reference to the value of a [`State`].
+pub struct StateMutRef<'a, T: 'static> {
+    inner: <SyncStorage as AnyStorage>::Mut<'a, StateValue<T>>,
+    did_deref_mut: bool,
+}
+
+impl<'a, T: 'static> ops::Deref for StateMutRef<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner.value
+    }
+}
+
+impl<'a, T: 'static> ops::DerefMut for StateMutRef<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.did_deref_mut = true;
+        &mut self.inner.value
+    }
+}
+
+impl<'a, T: 'static> Drop for StateMutRef<'a, T> {
+    fn drop(&mut self) {
+        if self.did_deref_mut {
+            self.inner.did_change = true;
+            if let Some(waker) = self.inner.waker.take() {
+                waker.wake();
+            }
+        }
+    }
+}
+
 /// `State` is a copyable wrapper for a value that can be observed for changes. States used by a
 /// component will cause the component to be re-rendered when its value changes.
 pub struct State<T: Send + Sync + 'static> {
@@ -132,14 +164,14 @@ impl<T: Sync + Send + 'static> Copy for State<T> {}
 impl<T: Copy + Sync + Send + 'static> State<T> {
     /// Gets a copy of the current value of the state.
     pub fn get(&self) -> T {
-        self.inner.read().value
+        *self.read()
     }
 }
 
 impl<T: Sync + Send + 'static> State<T> {
     /// Sets the value of the state.
     pub fn set(&mut self, value: T) {
-        self.modify(|v| *v = value);
+        *self.write() = value;
     }
 
     /// Returns a reference to the state's value.
@@ -148,33 +180,37 @@ impl<T: Sync + Send + 'static> State<T> {
     /// multiple copies of the same state, writes to one will be blocked for as long as any
     /// reference returned by this method exists.</div>
     pub fn read(&self) -> StateRef<T> {
-        StateRef {
-            inner: self.inner.read(),
+        loop {
+            match self.inner.try_read() {
+                Ok(inner) => break StateRef { inner },
+                Err(BorrowError::AlreadyBorrowedMut(_)) => self.inner.write(),
+                Err(BorrowError::Dropped(_)) => panic!("state was read after owner was dropped"),
+            };
         }
     }
 
-    fn modify<F>(&mut self, f: F)
-    where
-        F: FnOnce(&mut T),
-    {
-        let mut inner = self.inner.write();
-        f(&mut inner.value);
-        inner.did_change = true;
-        if let Some(waker) = inner.waker.take() {
-            waker.wake();
+    /// Returns a mutable reference to the state's value.
+    ///
+    /// <div class="warning">It is possible to create a deadlock using this method. If you have
+    /// multiple copies of the same state, operations on one will be blocked for as long as any
+    /// reference returned by this method exists.</div>
+    pub fn write(&mut self) -> StateMutRef<T> {
+        StateMutRef {
+            inner: self.inner.write(),
+            did_deref_mut: false,
         }
     }
 }
 
 impl<T: Debug + Sync + Send + 'static> Debug for State<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        self.inner.read().value.fmt(f)
+        self.read().fmt(f)
     }
 }
 
 impl<T: Display + Sync + Send + 'static> Display for State<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        self.inner.read().value.fmt(f)
+        self.read().fmt(f)
     }
 }
 
@@ -188,7 +224,7 @@ impl<T: ops::Add<Output = T> + Copy + Sync + Send + 'static> ops::Add<T> for Sta
 
 impl<T: ops::AddAssign<T> + Copy + Sync + Send + 'static> ops::AddAssign<T> for State<T> {
     fn add_assign(&mut self, rhs: T) {
-        self.modify(|v| *v += rhs);
+        *self.write() += rhs;
     }
 }
 
@@ -202,7 +238,7 @@ impl<T: ops::Sub<Output = T> + Copy + Sync + Send + 'static> ops::Sub<T> for Sta
 
 impl<T: ops::SubAssign<T> + Copy + Sync + Send + 'static> ops::SubAssign<T> for State<T> {
     fn sub_assign(&mut self, rhs: T) {
-        self.modify(|v| *v -= rhs);
+        *self.write() -= rhs;
     }
 }
 
@@ -216,7 +252,7 @@ impl<T: ops::Mul<Output = T> + Copy + Sync + Send + 'static> ops::Mul<T> for Sta
 
 impl<T: ops::MulAssign<T> + Copy + Sync + Send + 'static> ops::MulAssign<T> for State<T> {
     fn mul_assign(&mut self, rhs: T) {
-        self.modify(|v| *v *= rhs);
+        *self.write() *= rhs;
     }
 }
 
@@ -230,34 +266,31 @@ impl<T: ops::Div<Output = T> + Copy + Sync + Send + 'static> ops::Div<T> for Sta
 
 impl<T: ops::DivAssign<T> + Copy + Sync + Send + 'static> ops::DivAssign<T> for State<T> {
     fn div_assign(&mut self, rhs: T) {
-        self.modify(|v| *v /= rhs);
+        *self.write() /= rhs;
     }
 }
 
 impl<T: cmp::PartialEq<T> + Sync + Send + 'static> cmp::PartialEq<T> for State<T> {
     fn eq(&self, other: &T) -> bool {
-        self.inner.read().value == *other
+        *self.read() == *other
     }
 }
 
 impl<T: cmp::PartialOrd<T> + Sync + Send + 'static> cmp::PartialOrd<T> for State<T> {
     fn partial_cmp(&self, other: &T) -> Option<cmp::Ordering> {
-        self.inner.read().value.partial_cmp(other)
+        self.read().partial_cmp(other)
     }
 }
 
 impl<T: cmp::PartialEq<T> + Sync + Send + 'static> cmp::PartialEq<State<T>> for State<T> {
     fn eq(&self, other: &State<T>) -> bool {
-        self.inner.read().value == other.inner.read().value
+        *self.read() == *other.read()
     }
 }
 
 impl<T: cmp::PartialOrd<T> + Sync + Send + 'static> cmp::PartialOrd<State<T>> for State<T> {
     fn partial_cmp(&self, other: &State<T>) -> Option<cmp::Ordering> {
-        self.inner
-            .read()
-            .value
-            .partial_cmp(&other.inner.read().value)
+        self.read().partial_cmp(&other.read())
     }
 }
 
@@ -307,5 +340,10 @@ mod tests {
         assert!(state > 42);
         assert!(state >= 43);
         assert!(state < 44);
+
+        assert_eq!(*state.write(), 43);
+
+        let state_copy = state.clone();
+        assert_eq!(*state.read(), *state_copy.read());
     }
 }