Finished basic google home implementation with some slight refactors along the way

impl_cast/src/lib.rs

@@ -0,0 +1,31 @@
+pub extern crate paste;
+
+#[macro_export]
+macro_rules! impl_cast {
+    ($base:ident, $trait:ident) => {
+        $crate::paste::paste! {
+            pub trait [< As $trait>] {
+                fn cast(&self) -> Option<&dyn $trait>;
+                fn cast_mut(&mut self) -> Option<&mut dyn $trait>;
+            }
+
+            impl<T: $base> [< As $trait>] for T {
+                default fn cast(&self) -> Option<&dyn $trait> {
+                    None
+                }
+                default fn cast_mut(&mut self) -> Option<&mut dyn $trait> {
+                    None
+                }
+            }
+
+            impl<T: $base + $trait> [< As $trait>] for T {
+                fn cast(&self) -> Option<&dyn $trait> {
+                    Some(self)
+                }
+                fn cast_mut(&mut self) -> Option<&mut dyn $trait> {
+                    Some(self)
+                }
+            }
+        }
+    };
+}