c++templatesc++11type-traitstdm-mingw

Compile time Restricted Templates without use of boost


this is related to these two questions:

  1. standard c++11 way to remove all pointers of a type
  2. Compile Time Template restriction C++

the second one is mine

the issue is when i moved to TDM-GCC 64 the following code (previously working) does not compile I made sure c++11 is enabled.

I took the remove_all_pointers from the first question, and combined it with the answer to my question(bullet #2).

The following is my (previously) compilable example

#include <iostream>
#include <type_traits>

using namespace std;

template <typename T> class remove_all_pointers{
public:
    typedef T type;
};

template <typename T> class remove_all_pointers<T*>{
public:
    typedef typename remove_all_pointers<T>::type type;
};

template <typename T> class remove_all_pointers<T* const>{
public:
    typedef typename remove_all_pointers<T>::type type;
};

template <typename T> class remove_all_pointers<T* volatile>{
public:
    typedef typename remove_all_pointers<T>::type type;
};

template <typename T> class remove_all_pointers<T* const volatile >{
public:
    typedef typename remove_all_pointers<T>::type type;
};


class OverVoid{
public:

    static bool isOverVoid (){
    return true;
    }
    virtual ~OverVoid(){
    }
};

class Meta: public OverVoid{

};

class Physical{
public:

};

template<typename _Ty,typename = typename std::enable_if<std::is_base_of<OverVoid, remove_all_pointers<_Ty>::type>::value>::type>

class Move{
public:
    Move()
    {
        cout<<"### "<<remove_all_pointers<_Ty>::type::isOverVoid()<<endl;
    }
};


template<typename _Ty,typename = typename std::enable_if<std::is_base_of<OverVoid, remove_all_pointers<_Ty>::type>::value>::type>

class Move{
public:
    Move()
    {
        cout<<"### "<<remove_all_pointers<_Ty>::type::isOverVoid()<<endl;
    }
};




    template<typename _Ty,
    typename enable_if< is_base_of<OverVoid, remove_all_pointers<_Ty>::type>::value>::type>
    class Move{
    public:
        Move()
        {
            cout<<"### "<<remove_all_pointers<_Ty>::type::isOverVoid()<<endl;
        }
    };


    int main(){

        Move<Meta***> z;
        Move<Meta**> w;
        Move<Meta*> x;
        Move<Meta> y;

    }

it displays the following error

Info: Internal Builder is used for build
g++ -std=c++0x -std=c++11 -std=gnu++11 -O0 -g3 -Wall -c -fmessage-length=0 -o "src\\helllo_world.o" "..\\src\\helllo_world.cpp" 
In file included from ..\src\helllo_world.cpp:1:0:
..\src\Move.h:54:111: error: type/value mismatch at argument 2 in template parameter list for 'template<class, class> struct std::is_base_of'
 template<typename _Ty,class = typename std::enable_if<std::is_base_of<OverVoid, remove_all_pointers<_Ty>::type>::value>::type>
                                                                                                               ^
..\src\Move.h:54:111: note:   expected a type, got 'remove_all_pointers<T>::type'
..\src\Move.h:54:119: error: template argument 1 is invalid
 template<typename _Ty,class = typename std::enable_if<std::is_base_of<OverVoid, remove_all_pointers<_Ty>::type>::value>::type>
                                                                                                                       ^
..\src\helllo_world.cpp: In function 'int main()':
..\src\helllo_world.cpp:31:14: error: template argument 2 is invalid
  Move<Meta***> z;
              ^
..\src\helllo_world.cpp:32:13: error: template argument 2 is invalid
  Move<Meta**> w;
             ^
..\src\helllo_world.cpp:33:12: error: template argument 2 is invalid
  Move<Meta*> x;
            ^
..\src\helllo_world.cpp:34:11: error: template argument 2 is invalid
  Move<Meta> y;
           ^
..\src\helllo_world.cpp:31:16: warning: unused variable 'z' [-Wunused-variable]
  Move<Meta***> z;
                ^
..\src\helllo_world.cpp:32:15: warning: unused variable 'w' [-Wunused-variable]
  Move<Meta**> w;
               ^
..\src\helllo_world.cpp:33:14: warning: unused variable 'x' [-Wunused-variable]
  Move<Meta*> x;
              ^
..\src\helllo_world.cpp:34:13: warning: unused variable 'y' [-Wunused-variable]
  Move<Meta> y;
             ^

Solution

  • You are missing some typenames and have the class template Move definition repeated three times.

    Th below code works:

    #include <iostream>
    #include <type_traits>
    
    using namespace std;
    
    template <typename T> class remove_all_pointers{
    public:
        typedef T type;
    };
    
    template <typename T> class remove_all_pointers<T*>{
    public:
        typedef typename remove_all_pointers<T>::type type;
    };
    
    template <typename T> class remove_all_pointers<T* const>{
    public:
        typedef typename remove_all_pointers<T>::type type;
    };
    
    template <typename T> class remove_all_pointers<T* volatile>{
    public:
        typedef typename remove_all_pointers<T>::type type;
    };
    
    template <typename T> class remove_all_pointers<T* const volatile >{
    public:
        typedef typename remove_all_pointers<T>::type type;
    };
    
    
    class OverVoid{
    public:
    
        static bool isOverVoid (){
        return true;
        }
        virtual ~OverVoid(){
        }
    };
    
    class Meta: public OverVoid{
    
    };
    
    class Physical{
    public:
    
    };
    
    template<typename T, typename = typename std::enable_if<std::is_base_of<OverVoid, typename remove_all_pointers<T>::type>::value>::type>
    class Move{
    public:
        Move()
        {
            cout<<"### "<<remove_all_pointers<T>::type::isOverVoid()<<endl;
        }
    };
    
    /*
    template<typename T,typename = typename std::enable_if<std::is_base_of<OverVoid, typename remove_all_pointers<T>::type>::value>::type>
    class Move{
    public:
        Move()
        {
            cout<<"### "<<remove_all_pointers<T>::type::isOverVoid()<<endl;
        }
    };
    
    template<typename T, typename = typename std::enable_if<std::is_base_of<OverVoid, typename remove_all_pointers<T>::type>::value>::type>
    class Move{
    public:
        Move()
        {
            cout<<"### "<<remove_all_pointers<T>::type::isOverVoid()<<endl;
        }
    };
    */
    
    int main(){
        Move<Meta***> z;
        Move<Meta**> w;
        Move<Meta*> x;
        Move<Meta> y;
    }
    

    Live demo here.