Exit signal gets its own trait (#433)

* Exit signal gets its own trait

* Typo

* Removed clone bounds

substrate/polkadot/src/main.rs

@@ -38,11 +38,9 @@ mod vergen {
 
 // the regular polkadot worker simply does nothing until ctrl-c
 struct Worker;
-impl cli::Worker for Worker {
-	type Work = Self::Exit;
+impl cli::IntoExit for Worker {
 	type Exit = future::MapErr<oneshot::Receiver<()>, fn(oneshot::Canceled) -> ()>;
-
-	fn exit_only(&self) -> Self::Exit {
+	fn into_exit(self) -> Self::Exit {
 		// can't use signal directly here because CtrlC takes only `Fn`.
 		let (exit_send, exit) = oneshot::channel();
 
@@ -55,9 +53,13 @@ impl cli::Worker for Worker {
 
 		exit.map_err(drop)
 	}
+}
 
-	fn work<C: ServiceComponents>(self, _service: &Service<C>) -> Self::Exit {
-		self.exit_only()
+impl cli::Worker for Worker {
+	type Work = <Self as cli::IntoExit>::Exit;
+	fn work<C: ServiceComponents>(self, _service: &Service<C>) -> Self::Work {
+		use cli::IntoExit;
+		self.into_exit()
 	}
 }