问题描述
我想预先创建一个模板成员函数指针数组，它将使用在运行时由另一个类确定的变量进行索引。然后可以专门化模板函数。
这在非模板类中有效，但是我在模板类中遇到问题。应用程序有多个电源，为 MatchT 定义不同的模板参数，这在代码示例中是有希望的代表：
#include Data.H // POD对象。
template< typename MatchT>
class Manager
{
public：
template< int P>
bool do（Data& D_）;
template< int P，int ... Ps>
struct table：table< P-1，P-1，Ps ...> {};
template< int ... Ps>
结构表< 0，Ps ...>
{
static constexpr bool（* fns []）（Data&）= {do&Ps; ...}
};
};
template< typename MatchT>
template< int ... Ps>
constexpr bool（* Manager< MatchT> :: table< 0，Ps ...> :: fns [sizeof ...（Ps）]）
//process.h
#includeManager.H
模板< typename MatchT>
class Process
{
public：
void send（Manager< MatchT>& mgr）;
private：
typename Manager< MatchT> :: template table< 4> _processtable;
};
//process.c
模板< typename MatchT>
void Process< MatchT> :: send（Manager< MatchT>& mgr）
{
错误这里：
mgr。* _processtable :: fns [1]
}
ERROR：
在constexpr bool（* const Manager< MyManager< MyConfig>> :: table< 0,0,1,2,3& :: fns [4]（data&）
需要从process.C...
需要从manager.H错误没有匹配转换函数'do' bool（* const）（struct Data&）'
static constexpr bool（* fns []）（Data&）= {do&Ps; ...};
note：candidate is：template& int P> bool Manager< MatchT> :: do（Data&）[with int P = P; MatchT = DummyMatch]
需要从process.C...
manager.H错误没有匹配转换函数'do'到类型'bool（* const）（struct Data&）'
static constexpr bool（* fns []）（Data&）= {do& ...};
注意：候选是：template< int P> bool Manager< MatchT> :: do（Data&）[with int P = P; MatchT = MyMatch< MyConfig>我想知道是否有静态的 static constexpr bool（* fns []）（ Data&）= {do&Ps; ...}; 在模板类中引起问题。是否不能将每个 Manager< MatchT> 类型的函数定义为静态类型？解决方案您声明并定义了 fns 当它真的需要一个指向成员函数的指针数组时，函数的指针数组。尝试：
模板< typename MatchT>
class Manager
{
public：
template< int P>
bool do（Data& d_）;
template< int P，int ... Ps>
struct table：table< P-1，P-1，Ps ...> {};
template< int ... Ps>
struct table< 0，Ps ...>
{
static constexpr bool（Manager :: * fns []）（Data&）= {& Manager :: do&Ps; ...}
};
};
template< typename MatchT>
template< int ... Ps>
constexpr bool（Manager< MatchT> :: * Manager< MatchT> :: table< 0，Ps ...> :: fns [sizeof ...（Ps）]）
I want to pre create an array of template member function pointers, which will be indexed using a variable determined at run time by another class. The template functions can then be specialized.
This works in a non-template class, however I'm having issues in a template class. The applications has multiple mains which define different template arguments for MatchT, and this is hopefully representative in the code example:
#include Data.H // POD object. template<typename MatchT> class Manager { public: template <int P> bool do(Data& d_); template<int P, int ...Ps> struct table : table<P-1, P-1, Ps... >{}; template<int... Ps> struct table <0, Ps...> { static constexpr bool(*fns[])(Data&)={do<Ps>...}; }; }; template <typename MatchT> template<int... Ps> constexpr bool(*Manager<MatchT>::table<0,Ps...>::fns[sizeof...(Ps)])(); //process.h #include "Manager.H" template<typename MatchT> class Process { public: void send(Manager<MatchT>& mgr ); private: typename Manager<MatchT>::template table<4> _processtable; }; //process.c template<typename MatchT> void Process<MatchT>::send(Manager<MatchT>& mgr) { ERROR here: mgr.*_processtable::fns[1](); } ERROR: In instantiation of "constexpr bool (* const Manager<MyManager<MyConfig> >::table<0,0,1,2,3>::fns[4](Data&) required from "process.C"... required from "manager.H" error no matches converting function 'do' to type 'bool (* const)(struct Data&)' static constexpr bool(*fns[])(Data&) = {do<Ps>...}; note:candidate is: template<int P> bool Manager<MatchT>::do(Data&) [with int P = P; MatchT = DummyMatch] required from "process.C"... required from "manager.H" error no matches converting function 'do' to type 'bool (* const)(struct Data&)' static constexpr bool(*fns[])(Data&) = {do<Ps>...}; note:candidate is: template<int P> bool Manager<MatchT>::do(Data&) [with int P = P; MatchT = MyMatch<MyConfig> >]I'm wondering if having the static static constexpr bool(*fns[])(Data&)={do<Ps>...}; in the template class is causing an issue. Is it not able to define the functions as static for each Manager<MatchT> type? What am I missing?
解决方案You declared and defined fns as an array of pointers to functions, when it really needs to be an array of pointers to member functions. Try:
template<typename MatchT> class Manager { public: template <int P> bool do(Data& d_); template<int P, int ...Ps> struct table : table<P-1, P-1, Ps... >{}; template<int... Ps> struct table <0, Ps...> { static constexpr bool(Manager::*fns[])(Data&)={&Manager::do<Ps>...}; }; }; template <typename MatchT> template<int... Ps> constexpr bool(Manager<MatchT>::*Manager<MatchT>::table<0,Ps...>::fns[sizeof...(Ps)])(Data&);
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