Optimize Buffer::set_rich_text for when the buffer is reconstructed

src/cached.rs

@@ -0,0 +1,71 @@
+use core::fmt::Debug;
+
+/// Helper for caching a value when the value is optionally present in the 'unused' state.
+#[derive(Clone, Debug)]
+pub enum Cached<T: Clone + Debug> {
+    Empty,
+    Unused(T),
+    Used(T),
+}
+
+impl<T: Clone + Debug> Cached<T> {
+    pub fn get(&self) -> Option<&T> {
+        match self {
+            Self::Empty | Self::Unused(_) => None,
+            Self::Used(t) => Some(t),
+        }
+    }
+
+    pub fn get_mut(&mut self) -> Option<&mut T> {
+        match self {
+            Self::Empty | Self::Unused(_) => None,
+            Self::Used(t) => Some(t),
+        }
+    }
+
+    pub fn is_unused(&self) -> bool {
+        match self {
+            Self::Empty | Self::Unused(_) => true,
+            Self::Used(_) => false,
+        }
+    }
+
+    pub fn is_used(&self) -> bool {
+        match self {
+            Self::Empty | Self::Unused(_) => false,
+            Self::Used(_) => true,
+        }
+    }
+
+    pub fn take_unused(&mut self) -> Option<T> {
+        if matches!(*self, Self::Unused(_)) {
+            let Self::Unused(val) = std::mem::replace(self, Self::Empty) else {
+                unreachable!()
+            };
+            Some(val)
+        } else {
+            None
+        }
+    }
+
+    pub fn take_used(&mut self) -> Option<T> {
+        if matches!(*self, Self::Used(_)) {
+            let Self::Used(val) = std::mem::replace(self, Self::Empty) else {
+                unreachable!()
+            };
+            Some(val)
+        } else {
+            None
+        }
+    }
+
+    pub fn set_unused(&mut self) {
+        if matches!(*self, Self::Used(_)) {
+            *self = Self::Unused(self.take_used().unwrap());
+        }
+    }
+
+    pub fn set_used(&mut self, val: T) {
+        *self = Self::Used(val);
+    }
+}