Rewrite Rhai function dispatching

src/any.rs

@@ -0,0 +1,102 @@
+use std::any::{Any as StdAny, TypeId};
+use std::fmt;
+
+pub trait Any: StdAny {
+    fn type_id(&self) -> TypeId;
+
+    fn box_clone(&self) -> Box<Any>;
+
+    /// This type may only be implemented by `rhai`.
+    #[doc(hidden)]
+    fn _closed(&self) -> _Private;
+}
+
+impl<T> Any for T
+    where
+        T: Clone + StdAny + ?Sized
+{
+    #[inline]
+    fn type_id(&self) -> TypeId {
+        TypeId::of::<T>()
+    }
+
+    #[inline]
+    fn box_clone(&self) -> Box<Any> {
+        Box::new(self.clone())
+    }
+
+    fn _closed(&self) -> _Private {
+        _Private
+    }
+}
+
+impl Any {
+    #[inline]
+    fn box_clone(&self) -> Box<Any> {
+        Any::box_clone(self)
+    }
+
+    #[inline]
+    pub fn is<T: Any>(&self) -> bool {
+        let t = TypeId::of::<T>();
+        let boxed = self.type_id();
+
+        t == boxed
+    }
+
+    #[inline]
+    pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
+        if self.is::<T>() {
+            unsafe {
+                Some(&*(self as *const Any as *const T))
+            }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
+        if self.is::<T>() {
+            unsafe {
+                Some(&mut *(self as *mut Any as *mut T))
+            }
+        } else {
+            None
+        }
+    }
+}
+
+impl Clone for Box<Any> {
+    fn clone(&self) -> Self {
+        Any::box_clone(self.as_ref() as &Any)
+    }
+}
+
+impl fmt::Debug for Any {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Any")
+    }
+}
+
+pub trait AnyExt: Sized {
+    fn downcast<T: Any + Clone>(self) -> Result<Box<T>, Self>;
+}
+
+impl AnyExt for Box<Any> {
+    fn downcast<T: Any + Clone>(self) -> Result<Box<T>, Self> {
+        if self.is::<T>() {
+            unsafe {
+                let raw: *mut Any = Box::into_raw(self);
+                Ok(Box::from_raw(raw as *mut T))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+/// Private type which ensures that `rhai::Any` can only
+/// be implemented by this crate.
+#[doc(hidden)]
+pub struct _Private;