From 7aba2833df2f9ef2e5636571e95abefb0c1cc67d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastian=20K=C3=B6cher?= <git@kchr.de>
Date: Mon, 12 Feb 2018 20:41:47 +0100
Subject: [PATCH] Adds `transition!` macro to simplify state transitions

---
 README.md           | 17 ++++++++++++++---
 src/lib.rs          | 19 ++++++++++++++++---
 src/transition.rs   |  5 +++++
 tests/into_after.rs |  9 ++++++++-
 4 files changed, 43 insertions(+), 7 deletions(-)
 create mode 100644 src/transition.rs

diff --git a/README.md b/README.md
index 7ee2584..1e6d705 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,7 @@ boilerplate for you.
 * [Guide](#guide)
 * [Example](#example)
 * [Attributes](#attributes)
+* [Macro](#macro)
 * [Features](#features)
 * [License](#license)
 * [Contribution](#contribution)
@@ -335,7 +336,7 @@ impl PollGame for Game {
             active: invite.from,
             idle: invite.to,
         };
-        Ok(Async::Ready(waiting.into()))
+        transition!(waiting)
     }
 
     fn poll_waiting_for_turn<'a>(
@@ -352,8 +353,7 @@ impl PollGame for Game {
         // and request the turn over HTTP.
         let waiting = waiting.take();
         if let Some(game_result) = process_turn(turn) {
-            let finished = Finished(game_result);
-            Ok(Async::Ready(finished.into()))
+            transition!(Finished(game_result))
         } else {
             let next_waiting = WaitingForTurn {
                 turn: waiting.idle.request_turn(),
@@ -407,6 +407,17 @@ generated `Future` implementation uses the field's type as `Future::Error`.
 a variant of the state machine description `enum`. Describes the states that
 this one can transition to.
 
+### Macro
+
+An auxiliary macro is provided that helps reducing boilerplate code for state
+transitions. So, the following code:
+
+```Ok(Ready(NextState(1).into()))```
+
+Can be reduced to:
+
+```transition!(NextState(1))```
+
 ### Features
 
 Here are the `cargo` features that you can enable:
diff --git a/src/lib.rs b/src/lib.rs
index 78e1ead..c3172b7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,6 +12,7 @@ boilerplate for you.
 * [Guide](#guide)
 * [Example](#example)
 * [Attributes](#attributes)
+* [Macro](#macro)
 * [Features](#features)
 * [License](#license)
 * [Contribution](#contribution)
@@ -358,7 +359,7 @@ impl PollGame for Game {
             active: invite.from,
             idle: invite.to,
         };
-        Ok(Async::Ready(waiting.into()))
+        transition!(waiting)
     }
 
     fn poll_waiting_for_turn<'a>(
@@ -375,8 +376,7 @@ impl PollGame for Game {
         // and request the turn over HTTP.
         let waiting = waiting.take();
         if let Some(game_result) = process_turn(turn) {
-            let finished = Finished(game_result);
-            Ok(Async::Ready(finished.into()))
+            transition!(Finished(game_result))
         } else {
             let next_waiting = WaitingForTurn {
                 turn: waiting.idle.request_turn(),
@@ -435,6 +435,17 @@ generated `Future` implementation uses the field's type as `Future::Error`.
 a variant of the state machine description `enum`. Describes the states that
 this one can transition to.
 
+## Macro
+
+An auxiliary macro is provided that helps reducing boilerplate code for state
+transitions. So, the following code:
+
+```Ok(Ready(NextState(1).into()))```
+
+Can be reduced to:
+
+```transition!(NextState(1))```
+
 ## Features
 
 Here are the `cargo` features that you can enable:
@@ -483,6 +494,8 @@ extern crate derive_state_machine_future;
 pub use derive_state_machine_future::*;
 
 mod compile_fail_tests;
+#[macro_use]
+mod transition;
 
 /// Re-export of `rent_to_own::RentToOwn`.
 pub type RentToOwn<'a, T> = rent_to_own::RentToOwn<'a, T>;
diff --git a/src/transition.rs b/src/transition.rs
new file mode 100644
index 0000000..be3f263
--- /dev/null
+++ b/src/transition.rs
@@ -0,0 +1,5 @@
+/// Auxiliary macro for `poll_state_xy` functions to transition into a new state.
+#[macro_export]
+macro_rules! transition {
+    ( $new_state:expr ) => (return Ok(::futures::Async::Ready($new_state.into())));
+}
diff --git a/tests/into_after.rs b/tests/into_after.rs
index 65bee33..155c374 100644
--- a/tests/into_after.rs
+++ b/tests/into_after.rs
@@ -13,9 +13,12 @@ pub enum Machine {
     /// Choose which next state to go into depending on what start value is
     /// given.
     #[state_machine_future(start)]
-    #[state_machine_future(transitions(Ready))]
+    #[state_machine_future(transitions(Ready, TransitionMacro))]
     Start,
 
+    #[state_machine_future(transitions(Ready))]
+    TransitionMacro,
+
     #[state_machine_future(ready)] Ready(usize),
 
     #[state_machine_future(error)] Error(usize),
@@ -25,4 +28,8 @@ impl PollMachine for Machine {
     fn poll_start<'a>(_: &'a mut RentToOwn<'a, Start>) -> Poll<AfterStart, usize> {
         Ok(Async::Ready(Ready(1).into()))
     }
+
+    fn poll_transition_macro<'a>(_: &'a mut RentToOwn<'a, TransitionMacro>) -> Poll<AfterTransitionMacro, usize> {
+        transition!(Ready(2))
+    }
 }