handle Cache in 'Cache' struct

src/misc.rs

@@ -11,6 +11,7 @@ pub struct Point {
 
 #[wasm_bindgen]
 impl Point {
+    #[inline]
     pub fn new(x: f32, y: f32) -> Self { Self { x, y } }
 }
 
@@ -28,3 +29,56 @@ impl Chart {
         (self.convert)((x, y)).map(|(x, y)| Point::new(x, y))
     }
 }
+
+pub struct Cache<T> {
+    backing_data: Option<T>,
+    valid: bool,
+}
+
+impl<T> Cache<T> {
+    #[allow(dead_code)]
+    #[inline]
+    pub fn new(backing_data: T) -> Self {
+        Self {
+            backing_data: Some(backing_data),
+            valid: true,
+        }
+    }
+
+    #[inline]
+    pub fn new_empty() -> Self {
+        Self {
+            backing_data: None,
+            valid: false,
+        }
+    }
+
+    #[inline]
+    pub fn get(&self) -> &T {
+        if !self.valid {
+            panic!("self.valid is false, but get() method was called!")
+        }
+
+        match &self.backing_data {
+            Some(x) => x,
+            None => panic!("self.backing_data is None"),
+        }
+    }
+
+    #[inline]
+    pub fn set(&mut self, data: T) {
+        self.valid = true;
+        self.backing_data = Some(data);
+    }
+
+    #[inline]
+    pub fn invalidate(&mut self) {
+        self.valid = false;
+        self.backing_data = None;
+    }
+
+    #[inline]
+    pub fn is_valid(&self) -> bool {
+        self.valid
+    }
+}