在不使用 boost 的情况下编译时间受限的模板

Question

这与以下两个问题有关：

standard c++11 way to remove all pointers of a type

第二个是我的

问题是当我移动到 TDM-GCC 64 时，以下代码（以前工作）不编译我确保启用了 c++11。

我从第一个问题中提取了 remove_all_pointers，并将其与我的问题（项目符号 #2）的答案相结合。

下面是我（以前）编译的例子

#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;

    }

显示如下错误

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;
             ^

Answer 1

您 missing some typenames 并且 class 模板 Move 定义重复了三次。

以下代码有效：

#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.

在不使用 boost 的情况下编译时间受限的模板

Compile time Restricted Templates without use of boost

c++

templates

c++11

typetraits

tdm-mingw