fix: impl cast/cast_mut for Snapshot

src/snapshot.rs

@@ -1,9 +1,10 @@
 use std::{
-    any::Any,
+    any::{type_name, Any},
     cell::{Ref, RefCell},
 };
 
-use crate::{pane::Pane, AsAny, Renderer};
+use crate::{pane::Pane, AsAny, Error, Renderer, Result};
+
 /// A `Snapshot` struct captures the state of a renderer at three different points:
 /// initial (`init`), before any changes (`before`), and after changes have been applied (`after`).
 /// It is generic over `R` where `R` must implement the `Renderer` and `Clone` traits.
@@ -22,6 +23,7 @@ impl<R: Renderer + Clone + 'static> Renderer for Snapshot<R> {
     }
 }
 
+// TODO: enable Snapshot<R> to use impl_as_any macro.
 impl<R: Renderer + Clone + 'static> AsAny for Snapshot<R> {
     fn as_any(&self) -> &dyn Any {
         self
@@ -32,6 +34,25 @@ impl<R: Renderer + Clone + 'static> AsAny for Snapshot<R> {
     }
 }
 
+// TODO: enable Snapshot<R> to use impl_cast macro.
+impl<R: Renderer + Clone + 'static> Snapshot<R> {
+    pub fn cast_mut(renderer: &mut dyn crate::Renderer) -> Result<&mut Self> {
+        let snapshot = renderer
+            .as_any_mut()
+            .downcast_mut::<Self>()
+            .ok_or_else(|| Error::DowncastError(type_name::<Self>().to_string()))?;
+        Ok(snapshot)
+    }
+
+    pub fn cast(renderer: &dyn crate::Renderer) -> Result<&Self> {
+        let snapshot = renderer
+            .as_any()
+            .downcast_ref::<Self>()
+            .ok_or_else(|| Error::DowncastError(type_name::<Self>().to_string()))?;
+        Ok(snapshot)
+    }
+}
+
 impl<R: Renderer + Clone + 'static> Snapshot<R> {
     /// Constructs a new `Snapshot` instance with the given renderer. The `init`, `before`, and
     /// `after` states are all initialized with clones of the provided renderer.