From 19092cef069aaf287f5a74d486f97ac505b30c6f Mon Sep 17 00:00:00 2001
From: Thomas Kemmer <tkemmer@computer.org>
Date: Wed, 20 Feb 2019 21:42:12 +0100
Subject: [PATCH] Add fsm::row type (C++17 only).

---
 src/fsm.h                | 35 +++++++++++++++-
 tests/Makefile.am        |  1 +
 tests/test_basic_row.cpp |  7 +---
 tests/test_row.cpp       | 88 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 123 insertions(+), 8 deletions(-)
 create mode 100644 tests/test_row.cpp

diff --git a/src/fsm.h b/src/fsm.h
index dc98cc7..221adc1 100644
--- a/src/fsm.h
+++ b/src/fsm.h
@@ -258,7 +258,7 @@ namespace fsmlite {
                 detail::invoke_as_binary_fn(action, self, event);
             }
 
-            // clang++-50: constexpr function's return type 'void' is not a literal type
+            // clang++-5.0: constexpr function's return type 'void' is not a literal type
             static /*constexpr*/ void process_event(std::nullptr_t, Derived& self, const Event& event) {
             }
 
@@ -299,7 +299,6 @@ namespace fsmlite {
          *
          * @tparam guard a static `Guard` instance
          */
-
         template<
             State start,
             class Event,
@@ -355,6 +354,38 @@ namespace fsmlite {
             }
         };
 
+#if __cplusplus >= 201703L
+        /**
+         * Generic transition class template (requires C++17).
+         *
+         * @tparam start the start state of the transition
+         *
+         * @tparam Event the event type triggering the transition
+         *
+         * @tparam target the target state of the transition
+         *
+         * @tparam action a static action function pointer, or `nullptr`
+         *
+         * @tparam guard a static guard function pointer, or `nullptr`
+         */
+        template<
+            State start,
+            class Event,
+            State target,
+            auto action = nullptr,
+            auto guard = nullptr
+        >
+        struct row : public row_base<start, Event, target> {
+            static void process_event(Derived& self, const Event& event) {
+                row_base<start, Event, target>::process_event(action, self, event);
+            }
+
+            static bool check_guard(const Derived& self, const Event& event) {
+                return row_base<start, Event, target>::check_guard(guard, self, event);
+            }
+        };
+#endif
+
     private:
         template<class Event, class...> struct by_event_type;
 
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 9c75a68..ed2c7cd 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -8,6 +8,7 @@ check_PROGRAMS = \
 	test_mem_fn_row \
 	test_notrans \
 	test_recursive \
+	test_row \
 	test_scoped \
 	test_traits
 
diff --git a/tests/test_basic_row.cpp b/tests/test_basic_row.cpp
index 92db947..3770537 100644
--- a/tests/test_basic_row.cpp
+++ b/tests/test_basic_row.cpp
@@ -1,11 +1,7 @@
 #include <cassert>
-#include <functional>
-#include <iostream>
 
 #include "fsm.h"
 
-using namespace std::placeholders;
-
 int value = 0;
 
 // global actions
@@ -48,12 +44,11 @@ class state_machine: public fsmlite::fsm<state_machine> {
     basic_row< Running, event, Running, decltype(&m::store2), &m::store2, decltype(&m::is2), &m::is2 >,
     basic_row< Running, event, Running, decltype(&m::store3), &m::store3, decltype(&m::is3), &m::is3 >,
     basic_row< Running, event, Exit,    decltype(&clear),     &clear      /* fallback */             >,
-    basic_row< Exit,    event, Exit,    decltype(nullptr),    nullptr                                >
+    basic_row< Exit,    event, Exit                                                                  >
 //  ----------+--------+------+--------+---------------------+-----------+------------------+-------+-
     >;
 };
 
-
 int main()
 {
     state_machine m;
diff --git a/tests/test_row.cpp b/tests/test_row.cpp
new file mode 100644
index 0000000..eb5cbb4
--- /dev/null
+++ b/tests/test_row.cpp
@@ -0,0 +1,88 @@
+#include <cassert>
+
+#include "fsm.h"
+
+#if __cplusplus >= 201703L
+
+int value = 0;
+
+// global actions
+
+void store(int i) { value = i; }
+void clear() { value = 0; }
+
+// global guards
+
+bool is1(int i) { return i == 1; }
+
+// fsm
+
+class state_machine: public fsmlite::fsm<state_machine> {
+    friend class fsm;  // base class needs access to transition_table
+
+public:
+    enum states { Init, Running, Exit };
+
+    using event = int;
+
+public:
+
+    static void store2() { value = 2; }
+
+    static bool is2(int i) { return i == 2; }
+
+    void store3() { value = 3; }
+
+    bool is3(int i) const { return i == 3; }
+
+private:
+    using m = state_machine;
+
+    using transition_table = table<
+//       Start    Event  Target   Action      Guard
+//  ----+--------+------+--------+-----------+-------+-
+    row< Init,    event, Running, &store              >,
+    row< Running, event, Running, &store,     &is1    >,
+    row< Running, event, Running, &m::store2, &m::is2 >,
+    row< Running, event, Running, &m::store3, &m::is3 >,
+    row< Running, event, Exit,    &clear              >,
+    row< Exit,    event, Exit                         >
+//  ----+--------+------+--------+-----------+-------+-
+    >;
+};
+
+#endif
+
+int main()
+{
+#if __cplusplus >= 201703L
+    state_machine m;
+    assert(m.current_state() == state_machine::Init);
+    assert(value == 0);
+
+    m.process_event(42);
+    assert(m.current_state() == state_machine::Running);
+    assert(value == 42);
+
+    m.process_event(1);
+    assert(m.current_state() == state_machine::Running);
+    assert(value == 1);
+
+    m.process_event(2);
+    assert(m.current_state() == state_machine::Running);
+    assert(value == 2);
+
+    m.process_event(3);
+    assert(m.current_state() == state_machine::Running);
+    assert(value == 3);
+
+    m.process_event(42);
+    assert(m.current_state() == state_machine::Exit);
+    assert(value == 0);
+
+    m.process_event(42);
+    assert(m.current_state() == state_machine::Exit);
+    assert(value == 0);
+#endif
+    return 0;
+}