add reference_of!() macro

src/model/valid.rs

@@ -18,7 +18,7 @@ macro_rules! validate {
 /// It will check all supplied types and return `false` if none are matching.
 ///
 /// # Example
-/// ```
+/// ```ignore
 /// fn validate(&self) -> bool {
 ///     assert_reference_of!(self.owner, Person);
 ///     true