MSVC2015 更新 3 可变参数模板解决方法
MSVC2015 update 3 variadic template workaround
Visual Studio 2015 update 3 改进了对 C++11 的支持,但我遇到了奇怪的问题,我正在寻找解决方法。
使用 MSVC 为模板类型参数 ("fully defined types") 编译可变参数模板代码时一切正常,但如果我想使用模板模板参数 ("partially defined types"),结果将变得不正确。
#include <iostream>
using namespace std;
template <template<typename> class... TS>
struct PARTIAL {
static void test(std::ostream& out)
{
out << "PARTIAL-PROBLEM" << endl;
}
};
template <template<typename> class T>
struct PARTIAL<T>{
static void test(std::ostream& out)
{out << "PARTIAL-OK-END" << endl;}
};
template <template<typename> class T, template<typename> class... TS>
struct PARTIAL<T, TS...>{
static void test(std::ostream& out)
{
out << "PARTIAL-OK" << endl;
PARTIAL<TS...>::test(out);
}
};
template <class... TS>
struct FULL {
static void test(std::ostream& out)
{
out << "FULL-PROBLEM" << endl;
}
};
template <class T>
struct FULL<T>{
static void test(std::ostream& out)
{out << "FULL-OK-END" << endl;}
};
template <class T, class... TS>
struct FULL<T, TS...>{
static void test(std::ostream& out)
{
out << "FULL-OK" << endl;
FULL<TS...>::test(out);
}
};
template <typename T>
struct B{};
int main()
{
FULL<int, int, int>::test(cout);
PARTIAL<B, B, B>::test(cout);
return 0;
}
GCC5.3 (MINGW) 的输出:
FULL-OK
FULL-OK
FULL-OK-END
PARTIAL-OK
PARTIAL-OK
PARTIAL-OK-END
MSVC 的输出:
FULL-OK
FULL-OK
FULL-OK-END
PARTIAL-OK
PARTIAL-OK
PARTIAL-OK
PARTIAL-PROBLEM
MSVC 以不同的方式为完全定义的类型和部分生成代码。最好的解决方法是什么?
向递归案例添加另一个参数将确保它不会被选择用于终止案例:
template <template<typename> class T, template<typename> class T2, template<typename> class... TS>
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
struct PARTIAL<T, T2, TS...>{
// ^^^^
static void test(std::ostream& out)
{
out << "PARTIAL-OK" << endl;
PARTIAL<T2, TS...>::test(out);
^^^^
}
};
Visual Studio 2015 update 3 改进了对 C++11 的支持,但我遇到了奇怪的问题,我正在寻找解决方法。
使用 MSVC 为模板类型参数 ("fully defined types") 编译可变参数模板代码时一切正常,但如果我想使用模板模板参数 ("partially defined types"),结果将变得不正确。
#include <iostream>
using namespace std;
template <template<typename> class... TS>
struct PARTIAL {
static void test(std::ostream& out)
{
out << "PARTIAL-PROBLEM" << endl;
}
};
template <template<typename> class T>
struct PARTIAL<T>{
static void test(std::ostream& out)
{out << "PARTIAL-OK-END" << endl;}
};
template <template<typename> class T, template<typename> class... TS>
struct PARTIAL<T, TS...>{
static void test(std::ostream& out)
{
out << "PARTIAL-OK" << endl;
PARTIAL<TS...>::test(out);
}
};
template <class... TS>
struct FULL {
static void test(std::ostream& out)
{
out << "FULL-PROBLEM" << endl;
}
};
template <class T>
struct FULL<T>{
static void test(std::ostream& out)
{out << "FULL-OK-END" << endl;}
};
template <class T, class... TS>
struct FULL<T, TS...>{
static void test(std::ostream& out)
{
out << "FULL-OK" << endl;
FULL<TS...>::test(out);
}
};
template <typename T>
struct B{};
int main()
{
FULL<int, int, int>::test(cout);
PARTIAL<B, B, B>::test(cout);
return 0;
}
GCC5.3 (MINGW) 的输出:
FULL-OK
FULL-OK
FULL-OK-END
PARTIAL-OK
PARTIAL-OK
PARTIAL-OK-END
MSVC 的输出:
FULL-OK
FULL-OK
FULL-OK-END
PARTIAL-OK
PARTIAL-OK
PARTIAL-OK
PARTIAL-PROBLEM
MSVC 以不同的方式为完全定义的类型和部分生成代码。最好的解决方法是什么?
向递归案例添加另一个参数将确保它不会被选择用于终止案例:
template <template<typename> class T, template<typename> class T2, template<typename> class... TS>
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
struct PARTIAL<T, T2, TS...>{
// ^^^^
static void test(std::ostream& out)
{
out << "PARTIAL-OK" << endl;
PARTIAL<T2, TS...>::test(out);
^^^^
}
};