Data update

Task/Delegates/Rust/delegates-2.rs

@@ -0,0 +1,41 @@
+#![feature(specialization)]
+
+trait Thingable {
+    fn thing(&self) -> &str;
+}
+
+struct Delegator<T>(Option<T>);
+
+struct Delegate {}
+
+impl Thingable for Delegate {
+    fn thing(&self) -> &'static str {
+        "Delegate implementation"
+    }
+}
+
+impl<T> Thingable for Delegator<T> {
+    default fn thing(&self) -> &str {
+        "Default implementation"
+    }
+}
+
+impl<T: Thingable> Thingable for Delegator<T> {
+    fn thing(&self) -> &str {
+        self.0.as_ref().map(|d| d.thing()).unwrap_or("Default implmementation")
+    }
+}
+
+fn main() {
+    let d: Delegator<i32> = Delegator(None);
+    println!("{}", d.thing());
+
+    let d: Delegator<i32> = Delegator(Some(42));
+    println!("{}", d.thing());
+
+    let d: Delegator<Delegate> = Delegator(None);
+    println!("{}", d.thing());
+
+    let d: Delegator<Delegate> = Delegator(Some(Delegate {}));
+    println!("{}", d.thing());
+}