the from repr trait

x/src/lib.rs

@@ -24,4 +24,10 @@ import!(sub_xpat, xpat, "xpat");
 #[cfg(feature = "macros")]
 pub use sub_macros::{
     FromRepr
-};
+};
+
+#[cfg(feature = "macros")]
+pub trait FromRepr: Sized {
+    type Repr;
+    fn from_repr(repr: Self::Repr) -> Option<Self>;
+}