Added "any state" feature

include/boost/sml.hpp

@@ -1087,7 +1087,9 @@ template <class T, class, class... Ts>
 transitions<Ts...> get_state_mapping_impl(state_mappings<T, aux::type_list<Ts...>> *);
 template <class T, class TMappings, class TUnexpected>
 struct get_state_mapping {
-  using type = decltype(get_state_mapping_impl<T, TUnexpected>((TMappings *)0));
+  using type = aux::conditional_t<aux::is_same<decltype(get_state_mapping_impl<T, TUnexpected>((TMappings *)0)), transitions<TUnexpected>>::value, 
+      decltype(get_state_mapping_impl<_, TUnexpected>((TMappings *)0)), 
+      decltype(get_state_mapping_impl<T, TUnexpected>((TMappings *)0))>;
 };
 template <class S>
 transitions_sub<S> get_sub_state_mapping_impl(...);

test/ft/states.cpp

@@ -28,6 +28,7 @@ struct e7 {
 const auto idle = sml::state<class idle>;
 const auto s1 = sml::state<class s1>;
 const auto s2 = sml::state<class s2>;
+const auto any = sml::state<sml::_>;
 
 test terminate_state = [] {
   struct c {
@@ -215,6 +216,51 @@ test states_initial_entry_actions_with_events = [] {
                                       std::type_index(typeid(sml::anonymous))} == c_.entries);
 };
 
+test any_state = [] {
+  struct c {
+    auto operator()() {
+      using namespace sml;
+      auto action1 = [this]{ calls += "a1|"; };
+      auto action2 = [this]{ calls += "a2|"; };
+      auto action3 = [this]{ calls += "a3|"; };
+
+      // clang-format off
+      return make_transition_table(
+        any + event<e1> / action1,
+        any + event<e2> / action2,
+        any + event<e3> / action3 = idle,
+
+        *idle + event<e1> = s1,
+        s1 + event<e2> = s2,
+        s2 + event<e3> = s1
+      );
+      // clang-format on
+    }
+
+    std::string calls{};
+  };
+
+  sml::sm<c> sm{};
+  const c& c_ = sm;
+
+  sm.process_event(e1());
+  expect(sm.is(s1));
+  sm.process_event(e1());
+  expect(sm.is(s1));
+  sm.process_event(e2());
+  expect(sm.is(s2));
+  sm.process_event(e1());
+  expect(sm.is(s2));
+  sm.process_event(e2());
+  expect(sm.is(s2));
+  sm.process_event(e3());
+  expect(sm.is(s1));
+  sm.process_event(e3());
+  expect(sm.is(idle));
+
+  expect("a1|a1|a2|a3|" == c_.calls);
+};
+
 #if !defined(_MSC_VER)
 test state_names = [] {
   struct c {