Entry actions are not called during state machine initialization

[Ulenspiegel]

I've mentioned it in another issue, but only now tested it separately and making an issue of its own. When state machine is created and its initial state configuration is entered, no entry actions are called. Example:

#include <cstdio>
#include <cassert>
#include <boost/msm-lite.hpp>

namespace msm = boost::msm::lite;

using msm::state;
using msm::event;
using msm::sm;
using msm::make_transition_table;

struct e1 {};
struct e2 {};

state<class SubSubState1_1> ss1_1;
state<class SubSubState1_2> ss1_2;

struct SubState1 {
  SubState1() {}
  auto configure() const noexcept {
    using namespace msm;
    return make_transition_table(
        *ss1_1 + event<e1> = ss1_2,
        ss1_1 + msm::on_entry / [] { printf("Entering SS1_1.\n"); },
        ss1_2 + msm::on_entry / [] { printf("Entering SS1_2.\n"); },
        ss1_1 + msm::on_exit / [] { printf("Leaving SS1_1.\n"); },
        ss1_2 + msm::on_exit / [] { printf("Leaving SS1_2.\n"); }
    );
  }
};

state<class SubSubState2_1> ss2_1;
state<class SubSubState2_2> ss2_2;

struct SubState2 {
  SubState2() {}
  auto configure() const noexcept {
    using namespace msm;
    return make_transition_table(
        *ss2_1 + event<e1> = ss2_1,
        ss2_1 + msm::on_entry / [] { printf("Entering SS2_1.\n"); },
        ss2_2 + msm::on_entry / [] { printf("Entering SS2_2.\n"); },
        ss2_1 + msm::on_exit / [] { printf("Leaving SS2_1.\n"); },
        ss2_2 + msm::on_exit / [] { printf("Leaving SS2_2.\n"); }
    );
  }
};

state<sm<SubState1>> ss1;
state<sm<SubState2>> ss2;

struct TopState {
  TopState() {}
  auto configure() const noexcept {
    using namespace msm;
    return make_transition_table(
        *ss1 + event<e2> = ss2,
        ss1 + msm::on_entry / [] { printf("Entering SS1.\n"); },
        ss2 + msm::on_entry / [] { printf("Entering SS2.\n"); },
        ss1 + msm::on_exit / [] { printf("Leaving SS1.\n"); },
        ss2 + msm::on_exit / [] { printf("Leaving SS2.\n"); }
    );
  }
};

int main(int argc, char** argv) {
  SubState1 ss1_;
  sm<SubState1> ssm1_(ss1_);
  SubState2 ss2_;
  sm<SubState2> ssm2_(ss2_);
  TopState s_;
  sm<TopState> m(s_, ssm1_, ssm2_);
  assert(m.is(ss1));
  assert(ssm1_.is(ss1_1));
  return 0;
}

When ran, program shows nothing - asserts confirm that state machine entered desired configuration (ss1(ss1_1)), but entry actions were not called. Since entry actions set identity for states, machine will have not been initialized properly.

Introducing a dummy initial state and anonymous transition helps:

struct TopState {
  TopState() {}
  auto configure() const noexcept {
    using namespace msm;
    return make_transition_table(
        *"init"_s = ss1,
        ss1 + event<e2> = ss2,
        ss1 + msm::on_entry / [] { printf("Entering SS1.\n"); },
        ss2 + msm::on_entry / [] { printf("Entering SS2.\n"); },
        ss1 + msm::on_exit / [] { printf("Leaving SS1.\n"); },
        ss2 + msm::on_exit / [] { printf("Leaving SS2.\n"); }
    );
  }
};

Output:

Entering SS1_1.
Entering SS1.

I think action order is still incorrect (see #43), but states are initialized at least. It's not intuitive and error prone though, takes running into the bug to resort to the dummy state.

[kris-jusiak]

Fixed in 3a962b8