无法找出TSm_中违反了哪个规则。 Sm_被编译,TSm_不是:
区别在于TSm_是模板,而Sm_不是。
#include <boost/msm/back/state_machine.hpp>
#include <boost/msm/front/state_machine_def.hpp>
namespace msm = boost::msm;
namespace mpl = boost::mpl;
struct Event {};
class Sm_ : public msm::front::state_machine_def<Sm_>
{
public:
using Me = Sm_;
struct First : public msm::front::state<>
{};
using initial_state = First;
struct Second : public msm::front::state<>
{};
void trans(const Event& /*e*/)
{}
struct transition_table : public mpl::vector<
a_row<First, Event, Second, &Me::trans>
>
{};
};
using Sm = msm::back::state_machine<Sm_>;
// broken one
enum class Side : char
{
Buy = 0, Sell = 1
};
template <Side side>
class TSm_ : public msm::front::state_machine_def<TSm_<side>>
{
public:
using Me = TSm_<side>;
using Base = msm::front::state_machine_def<Me>;
using Base::a_row;
struct First : public msm::front::state<>
{};
using initial_state = First;
struct Second : public msm::front::state<>
{};
void trans(const Event& /*e*/)
{}
struct transition_table : public mpl::vector<
a_row<First, Event, Second, &Me::trans> // compilation is failed here
>
{};
};
template <Side side>
using TSm = msm::back::state_machine<TSm_<side>>;
请帮忙更新
我找到了如何使其编译的方法:由于a_row不是类型而是模板,因此其别名也应为模板
struct Begin {};
template <Side side>
class TSm_ : public msm::front::state_machine_def<TSm_<side>>
{
public:
//-----------------------------------------------------------------------------------------------------
using Me = TSm_<side>;
using Base = msm::front::state_machine_def<Me>;
template<
typename T1
, class Event
, typename T2
, void (Me::*action)(Event const&)
>
using a_row = typename Base::a_row;
//-----------------------------------------------------------------------------------------------------
struct First : public msm::front::state<>
{};
//-----------------------------------------------------------------------------------------------------
using initial_state = First;
//-----------------------------------------------------------------------------------------------------
struct Second : public msm::front::state<>
{};
//-----------------------------------------------------------------------------------------------------
void trans(const Begin& /*e*/)
{}
//-----------------------------------------------------------------------------------------------------
struct transition_table : public mpl::vector<
a_row<First, Begin, Second, &Me::trans>
>
{};
};
正确吗,这条规则2) An alias template is a template which, when specialized, is equivalent to the result of substituting the template arguments of the alias template for the template parameters in the type-id吗? 最佳答案
当您使用模板状态机类定义转换表时,可以使用安装了row
,a_row
和g_row
家族的functor前端。
参见https://www.boost.org/doc/libs/1_67_0/libs/msm/doc/HTML/ch03s03.html
如果使用functor前端,则无需关心msm::front::state_machine_def
的子类是否为模板。
这是根据您的代码而更新的代码:
#include <iostream>
#include <boost/msm/back/state_machine.hpp>
#include <boost/msm/front/state_machine_def.hpp>
// include functor_row
#include <boost/msm/front/functor_row.hpp>
namespace msm = boost::msm;
namespace msmf = msm::front;
namespace mpl = boost::mpl;
struct Event {};
// broken one
enum class Side : char
{
Buy = 0, Sell = 1
};
template <Side side>
class TSm_ : public msm::front::state_machine_def<TSm_<side>>
{
public:
using Me = TSm_<side>;
using Base = msm::front::state_machine_def<Me>;
struct First : public msm::front::state<>
{};
using initial_state = First;
struct Second : public msm::front::state<>
{};
// Replace the member function trans() with the functor trans.
struct trans {
template <class Fsm, class SourceState, class TargetState>
void operator()(Event const&, Fsm&, SourceState&, TargetState&) const {
std::cout << "called" << std::endl;
}
};
struct transition_table : public mpl::vector<
//from event to action, guard
msmf::Row <First, Event, Second, Me::trans, msmf::none >
// This is functor front-end
>
{};
};
template <Side side>
using TSm = msm::back::state_machine<TSm_<side>>;
int main() {
TSm<Side::Buy> sm;
sm.start();
sm.process_event(Event());
}
运行演示:https://wandbox.org/permlink/e9Qoc2xW3TTGhsmu
关于c++ - 无法使用模板参数编译boost元状态机,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/51288962/