trait definition and struct-tuple example

src/example.rs

@@ -0,0 +1,28 @@
+use crate::generic::{Field, Sum, Generic};
+
+
+struct IntPair {
+    a: i32,
+    b: i32
+}
+
+impl Generic for IntPair {
+    type Representation = Sum<Field<i32>, Field<i32>>;
+    fn generalize(self) -> Self::Representation {
+        Sum { 
+            left: Field { value: self.a },
+            right: Field { value: self.b }
+        }
+    }
+    fn specialize(rep: Self::Representation) -> Self {
+        let Sum {
+            left: Field { value: a },
+            right: Field { value: b },
+        } = rep;
+        IntPair { a, b }
+    }
+}
+
+fn convert(x: IntPair) -> (i32, i32) {
+    Generic::specialize(x.generalize())
+}